Added target definition for C files to OSX makefile

New hashing functions used in CPU Mining were not found during
compiling since they are C files and the OSX makefile lacked a target
definition for these. Also took the liberty of changing 'litecoin'
occurrences to 'gridcoin'.
Merge pull request #8 from Lederstrumpf/ImproveLinuxAndMacCompatibility

Added target definition for C files to OSX makefile