I've just replaced all palloc()/memset() pairs for getting zeroed-out memory with palloc0(). I doubt that this will show a significant speedup, but it fits better into the PostgreSQL memory model and reduces the lines of code.
retval = (text *) palloc (len + VARHDRSZ);
memset(retval,0x0,len + VARHDRSZ);
retval = (text *) palloc0 (len + VARHDRSZ);
The changes have been comitted to Github.