googletest version is not detected properly.

When doing this on Mac OS 10.12.6:

autoreconf -i && ./configure --with-gtest-source=/Users/thomson/devel/gtest-1.8.0

I get the following (note the version is not detected as 1.8.0, but rather as "googletest")

Google Test:
  GTEST_VERSION:   googletest
  GTEST_INCLUDES:  -I/Users/thomson/devel/gtest-1.8.0/googletest -I/Users/thomson/devel/gtest-1.8.0/googletest/include
  GTEST_LDFLAGS:   
  GTEST_LDADD:     $(top_builddir)/ext/gtest/libgtest.a
  GTEST_SOURCE:    /Users/thomson/devel/gtest-1.8.0/googletest