Cycles Standalone: Support for relative paths and string OSL parameters.

Patch by John Haddon.
Differential Revision: https://developer.blender.org/D418

intern/cycles/util/util_path.h

@@ -41,6 +41,7 @@ string path_filename(const string& path);
 string path_dirname(const string& path);
 string path_join(const string& dir, const string& file);
 string path_escape(const string& path);
+bool path_is_relative(const string& path);
 
 /* file info */
 bool path_exists(const string& path);