Integrate GoogleTest

[HerbertKoelman]

This might look like a good way to go.

Snippet:

include(ExternalProject)
ExternalProject_Add(googletest
    URL https://googletest.googlecode.com/files/gtest-1.7.0.zip
    URL_HASH SHA1=f85f6d2481e2c6c4a18539e391aa4ea8ab0394af
    INSTALL_COMMAND ""
)

ExternalProject_Get_Property(googletest binary_dir)
add_library(gtest UNKNOWN IMPORTED)
add_library(gtest_main UNKNOWN IMPORTED)
set_target_properties(gtest PROPERTIES
    IMPORTED_LOCATION ${binary_dir}/libgtest.a
)
set_target_properties(gtest_main PROPERTIES
    IMPORTED_LOCATION ${binary_dir}/libgtest_main.a
)
add_dependencies(gtest googletest)
add_dependencies(gtest_main googletest)