Fix #include for sys/file.h in src/ROSETTA/src/grammar.h

The absolute path provided in src/ROSETTA/src/grammar.h makes it difficult to compile ROSE when using a different compiler than the standard distributed with a system. I ran into trouble attempting to compile in Ubuntu 12.04 LTS, due to the need to use GCC 4.4 (rather than the system default 4.6). It wants to use a different sys/file.h, and thus compilation breaks at the grammar.h header include.

The patch restores the "relative path" lookup for that include file. I do not know which environments necessitated the atypical absolute-path #include, but perhaps it could be wrapped with an #if/#ifdef for those specific failure cases, if they still even exist.