Add an SHA1 implementation from RFC 3174
Use the bundled sha1 implementation instead of relying on openssl

This simplifies running tests on platforms where OpenSSL isn't
commonly available.
Use the local sha1 function names directly without compatibility defines
Remove the now unused -Wno-deprecated-declarations on OS X

This was only required for building with OpenSSL.
Set GTEST_HAS_TR1_TUPLE to 0 on msvc

This fixes building of gtest on msvc.

See e.g. http://stackoverflow.com/questions/8274588 for
more discussion on the matter.
Wrap the library names in codec_unittest LDFLAGS, for use with MSVC
Allow building tests on MSVC versions where stdint.h is missing

Of the supported MSVC versions, only 2008 actually is missing
stdint.h, it is included in MSVC since 2010.