(takes too long).

Add second run of cpp_unittest which verifies that descriptors are constructed lazily.  This is accomplished by avoiding any use of descriptors while testing a bunch of other operations, then checking at the end that descriptors have not been constructed.

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.