Added test case for ExactInferenceMethod
GP framework only needs eigen3 now
Fixed printing of gradient result
Updated GP regression integration test
Added SG_UNREF for prevent memory leak
Merge pull request #1057 from votjakovr/develop

GP framework only needs eigen3 now
fix doxygen errors
fix doxygen error
lua 5.1 compile error fixes
Issue #1042 - Cross-Product for lists of kernels