The word "zorkmid" was hard-coded in format strings all

over the place.

Often they would use
	"%ld zorkmid%s", amt, plur(amt)
but not consistently, so some of the hard-coded usage
could result in "1 zorkmids"

This adds the function
	currency(long)
to return the name of the currency, either plural
or singular depending on the argument passed to it.
That eliminates the need for the extra %s in the
format string and the use of the plur() macro.

include/extern.h

@@ -785,6 +785,7 @@ E int NDECL(doorganize);
 E int FDECL(count_unpaid, (struct obj *));
 E int FDECL(count_buc, (struct obj *,int));
 E void FDECL(carry_obj_effects, (struct obj *));
+E const char *FDECL(currency, (long));
 
 /* ### ioctl.c ### */