objdump print_debugging_info memory leaks

Fix memory leaks and do a general tidy of the code for printing coff
and stabs debug.

	* prdbg.c: Delete unnneeded forward function declarations.
	Delete unnecessary casts throughout.  Free all strings
	returned from pop_type throughout file.
	(struct pr_stack): Delete "num_parents".  Replace tests for
	"num_parents" non-zero with tests of "parents" non-NULL
	throughout.  Free "parents" before assigning, and set to NULL
	after freeing.  Remove const from "method".  Always strdup
	strings assigned to method, and free before assigning.
	(print_debugging_info): Free info.stack and info.filename.