ODBM_File can use the same T_PTROBJ typemap as the other ?DBM_File modules.

ODBM_File can use the same T_PTROBJ typemap as the other ?DBM_File modules.

This simplifies the RETVAL handling in TIEHASH, and makes the code closer
to the other 3 ?DBM_File modules. The difference in TIEHASH handling dates
back to 5.000, where only ODBM_File needed helper code around the dbm_open()
call. The other 3 were able to #define it as dbm_TIEHASH, and hence had no
CODE: section when first written.