In perly.y, change PL_parser to parser

In perly.y, change PL_parser to parser

All these code snippets are embedded inside a function
(perly.c:yyparse) that puts the current value of PL_parser in a local
variable named parser.  So the two are equivalent, but the latter
only has to access a local variable.

Before:

$ ls -ld perly.o
-rw-r--r--  1 sprout  staff  94748 Aug 22 06:12 perly.o

After:

$ ls -ld perly.o
-rw-r--r--  1 sprout  staff  94340 Aug 22 06:15 perly.o