changes for language-sepcific help by Philippe

changes for language-sepcific help by Philippe
Waroquiers <wao@cfmu.eurocontrol.be> applied and largely revised.

(language): Added a `help' member.
(arg_type): Added an at_end constant.
(plain_C_suffixes): Some items removed from here.
(Objc_suffixes): And put here (new constant).
(Ada_help, Asm_help, default_C_help, Cplusplus_help, Cjava_help,
Cobol_help, Erlang_help, Fortran_help, HTML_help, Lisp_help,
Makefile_help, Objc_help, Pascal_help, Perl_help, PHP_help,
PS_help, Prolog_help, Python_help, Scheme_help, TeX_help,
Texinfo_help, Yacc_help, auto_help, none-help, no_lang_help): New
constants.
(PS_functions, PS_suffixes): Renamed from Postscript_functions and
Postscript_suffixes.
(lang_names): Adapted to the new language structure, new language
"objc" added (was previously merged with "proc").
(print_language_names): Some help strings corrected.
(print_help): Now takes an argument and possibly prints lang help.
(print_help): Some help strings corrected.  Documents
language-specific help.
(main): Only print help after having parsed all the arguments.