Added four new functions as shortcuts to creating GHashes that use the
standard ptr/str/int/pair hash and compare functions.
GHash *BLI_ghash_ptr_new(const char *info);
GHash *BLI_ghash_str_new(const char *info);
GHash *BLI_ghash_int_new(const char *info);
GHash *BLI_ghash_pair_new(const char *info);
Replaced almost all occurrences of BLI_ghash_new() with one of the
above functions.