gdb/

gdb/
	Code cleanup.
	* skip.c (skip_function_command, skip_file_command, skip_info): Remove
	unused forward declarations.
	(skip_file_command): Make variables symtab and filename targets const.
	Use proper 0 vs. NULL constant everywhere.
	(skip_function_command): Use proper 0 vs. NULL constant everywhere.
	Include empty line after declarations.  Use GNU spacing in a comment.
	Do not use strlen for end of string check.
	(skip_info): Use proper 0 vs. NULL constant everywhere.  Add column 5
	comments.
	(skip_enable_command, skip_disable_command, skip_delete_command)
	(add_skiplist_entry): Use proper 0 vs. NULL constant everywhere.
	(function_pc_is_marked_for_skip): Make variable filename target const.
	Use proper 0 vs. NULL constant everywhere.  Fix GNU non-compliant
	comment formatting.
	(skip_re_set): Add empty line after function comment.  Use proper 0 vs.
	NULL constant everywhere.  Include empty line after declarations.  Make
	variable symtab target const.  Do not use strlen for end of string
	check.

gdb/doc/
	* gdbint.texinfo (Coding Standards) (C Usage): New rule for 0 vs. NULL.