Fix compile error on Cygwin, where int32 is typedefed to long instead of int, and the compiler can't figure out which overload of this method to use in that case.

(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.