Bundle full gtest package with protocol buffers.

Instead of bundling bits of the gtest code with protocol buffers and compiling it as part of the protobuf makefiles, bundle the verbatim gtest package and use it as a nested autoconf package.  This should make it much easier to update to the latest gtest release in the future, or use a non-bundled gtest.

[chandlerc, 2009-04-21 04:29:02]

LGTM

Out of curiosity, why not drop the gtest branch directly into your subversion
tree and always package it? I can see possible reasons, just wondered what yours
are. On at least two of my projects, they just always provide gtest in order to
have complete control over the dependencies.

Regarding the build, I actually really like this strategy upon looking at it.
The nice thing is that gtest isn't built at all until you actually need to build
tests; I'm not sure there is a "better" way to package this up. Just some random
comments below.

http://codereview.appspot.com/47042/diff/1/26
File Makefile.am (right):

http://codereview.appspot.com/47042/diff/1/26#newcode12
Line 12: DIST_SUBDIRS = gtest src
Any reason not to use $(subdirs) from AC_CONFIG_SUBDIRS here?

http://codereview.appspot.com/47042/diff/1/26#newcode21
Line 21: @(cd gtest && $(MAKE) $(AM_MAKEFLAGS) lib/libgtest.la
lib/libgtest_main.la)
Automake's manual indicates you shouldn't need the subshell here and below to
keep the cd local to the rule, but it wouldn't be the first time that manual has
misled me if that's not actually true.