Some cleanups on stap-probe.c

Some cleanups on stap-probe.c

This patch does some basic cleanups on the SystemTap SDT probes API.  It
removes spurious newlines, brackets, reindents some code, and do
explicit checks for NULL, NUL, and 0 where applicable.

2013-12-23  Sergio Durigan JUnior  <sergiodj@redhat.com>

	* stap-probe.c (struct stap_probe) <args_parsed>: Add comment.
	(stap_is_generic_prefix): Delete extra brackets.  Reindent.
	(stap_parse_register_operand): Remove spurious newlines.  Simplify
	code to parse special token.
	(stap_parse_argument_conditionally): Add gdb_assert.
	(stap_parse_argument_1): Likewise.  Explicitly check for NULL and
	NUL.
	(stap_parse_probe_arguments): Likewise.
	(handle_stap_probe): Likewise.  Reindent code.
	(get_stap_base_address): Explicitly check for NULL.
	(stap_get_probes): Likewise.  Reindent code.
	(stap_relocate): Explicitly check for 0.
	(stap_gen_info_probes_table_values): Likewise.