Added frac benchmark

    * Makefile.am: Added frac benchmark
    * Makefile.in: Regenerated
    * configure: Regenerated
    * configure.ac: Added frac benchmark
    * src/frac/Makefile.am: Added frac benchmark
    * src/frac/Makefile.in: Regenerated
    * src/frac/frac.c: Added frac benchmark