OSL improvements.
Relative texture paths in expression fixes

Signed-off-by: Marius Avram <marius.avram1309@gmail.com>
Merge pull request #515 from marius-avram/relative_paths_fixes

Relative texture paths in expression fixes
Fixed PR comments.
Force travis build.
Reverted changes in test_vector.cpp
Removed microfacet BTDF test scene.
Small fix
Merge pull request #513 from est77/OSL

OSL improvements.