SNOW-756 / VWR-23385 FIXED standalone LD_LIBRARY_PATH for unit tests

Used patch from https://jira.secondlife.com/secure/attachment/41586/SNOW-756-standalone_tests.diff

patching file indra/cmake/LLAddBuildTest.cmake
Hunk #1 succeeded at 259 with fuzz 2 (offset 1 line).

Added entry in doc/contributions.txt. No further changes.

originally commited to Snowglobe 2.1 at http://svn.secondlife.com/trac/linden/changeset/3515