Add test verifying that protoc accepts trailing backslashes on Windows, which some users claim doesn't work.  Seems to work on my machine.

for details.

nested autoconf package rather than as raw source.  This way we can
trivially update it again in the future.

Actually, this change doesn't even include gtest in protobuf's SVN.
Instead, we auto-download it when autogen.sh is invoked.  Note that
it will be included in release distributions, though.

TODO:
* Add a configure option to use the system's installed gtest rather
  than the bundled copy.  Apparently the gtest maintainers are working
  on some general-purpose autoconf macros which will do this
  automagically.
* Update MSVC project files.

generated code.

convention to use when printing errors.  Default is GCC, but Microsoft
Visual Studio is another option.  This allows errors to be clickable in
the MSVS error log.

All Languages
* Repeated fields of primitive types (types other that string, group, and
  nested messages) may now use the option [packed = true] to get a more
  efficient encoding.  In the new encoding, the entire list is written
  as a single byte blob using the "length-delimited" wire type.  Within
  this blob, the individual values are encoded the same way they would
  be normally except without a tag before each value (thus, they are
  tightly "packed").

C++
* UnknownFieldSet now supports STL-like iteration.
* Message interface has method ParseFromBoundedZeroCopyStream() which parses
  a limited number of bytes from an input stream rather than parsing until
  EOF.

Java
* Fixed bug where Message.mergeFrom(Message) failed to merge extensions.
* Message interface has new method toBuilder() which is equivalent to
  newBuilderForType().mergeFrom(this).
* All enums now implement the ProtocolMessageEnum interface.
* Setting a field to null now throws NullPointerException.
* Fixed tendency for TextFormat's parsing to overflow the stack when
  parsing large string values.  The underlying problem is with Java's
  regex implementation (which unfortunately uses recursive backtracking
  rather than building an NFA).  Worked around by making use of possesive
  quantifiers.

Python
* Updated RPC interfaces to allow for blocking operation.  A client may
  now pass None for a callback when making an RPC, in which case the
  call will block until the response is received, and the response
  object will be returned directly to the caller.  This interface change
  cannot be used in practice until RPC implementations are updated to
  implement it.

Patch from Monty Taylor <monty.taylor@gmail.com>.

parsing test in parser_unittest.cc existed.)

  bash-only features, and /bin/sh is not a symlink to bash on all systems.
* If an input file is a Windows absolute path (e.g. "C:\foo\bar.proto") and
  the import path only contains "." (or contains "." but does not contain
  the file), protoc incorrectly thought that the file was under ".", because
  it thought that the path was relative (since it didn't start with a slash).
  This has been fixed.

  2.0.2.
* Minor Tru64 fix.

protoc
* Enum values may now have custom options, using syntax similar to field
  options.
* Fixed bug where .proto files which use custom options but don't actually
  define them (i.e. they import another .proto file defining the options)
  had to explicitly import descriptor.proto.
* Adjacent string literals in .proto files will now be concatenated, like in
  C.

C++
* Generated message classes now have a Swap() method which efficiently swaps
  the contents of two objects.
* All message classes now have a SpaceUsed() method which returns an estimate
  of the number of bytes of allocated memory currently owned by the object.
  This is particularly useful when you are reusing a single message object
  to improve performance but want to make sure it doesn't bloat up too large.
* New method Message::SerializeAsString() returns a string containing the
  serialized data.  May be more convenient than calling
  SerializeToString(string*).
* In debug mode, log error messages when string-type fields are found to
  contain bytes that are not valid UTF-8.
* Fixed bug where a message with multiple extension ranges couldn't parse
  extensions.
* Fixed bug where MergeFrom(const Message&) didn't do anything if invoked on
  a message that contained no fields (but possibly contained extensions).
* Fixed ShortDebugString() to not be O(n^2).  Durr.
* Fixed crash in TextFormat parsing if the first token in the input caused a
  tokenization error.

Java
* New overload of mergeFrom() which parses a slice of a byte array instead
  of the whole thing.
* New method ByteString.asReadOnlyByteBuffer() does what it sounds like.
* Improved performance of isInitialized() when optimizing for code size.

Python
* Corrected ListFields() signature in Message base class to match what
  subclasses actually implement.
* Some minor refactoring.

Patch (mostly) by Vincent Choinière <Choiniere.Vincent@hydro.qc.ca>.

Patch from Frank Chu.