Improve documentation of pdumper; minor code cleanup

* src/emacs.c (usage_message): Add the --dump-file option.
(string_starts_with_p, find_argument): Functions removed; use
'argmatch' instead.
(PDUMP_FILE_ARG): Macro removed; use literal strings instead,
as with other command-line options.  Use HAVE_PDUMPER for cpp
conditionals which used PDUMP_FILE_ARG.
(load_pdump, main): Use 'argmatch' for "--dump-file" and
"--temacs" arguments, thus supporting the "-dump-file" and
"-temacs" variants, for consistency with other options.
(main): Remove the extra fatal error for using --dump-file in
unexec'ed Emacs: load_pdump does that anyway.
(standard_args): Add --dump-file and --temacs, with
appropriate priorities.

* etc/NEWS: Expand on the pdumper support.

* doc/emacs/cmdargs.texi (Initial Options): Document the
'--dump-file' command-line option.
1 job for master in 55 minutes and 36 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Test
failed #565
test-all

00:55:36

 
Name Stage Failure
failed
test-all Test
Makefile:309: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:284: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:960: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1