support for Perl packages

support for Perl packages
* etags.c (Perl_functions): Tag packages and use them in sub tags.
(get_tag): Return a pointer to the tag that is found.

 general cleanup and streamlining
* etags.c (LOOKING_AT): Use !intoken instead of iswhite.
(F_takeprec): Renamed from takeprec.  All callers changed.
(F_getit): Renamed from getit.  All callers changed.
(nocase_tail): Renamed from tail.  All callers changed.
(Ada_getit): Renamed from adagetit.  All callers changed.
(L_getit): Simplified by using get_tag.
(Perl_functions, Postscript_functions, erlang_attribute): Use the
modified LOOKING_AT.
(notinname): Removed '[' and added ')' to the recognised chars.
(LOOKING_AT, get_tag, PHP_functions): Use notinname.
(Ada_getit, Ada_funcs, Python_functions, Scheme_functions):
Clarified, using strneq or notinname.
(L_isdef, L_isquote): Removed.
(Lisp_functions, L_getit): Clarified.

 changes for standalone compilation
* etags.c: (P_): Renamed to __P for consistency with config.h.
[HAVE_CONFIG_H]: Let config.h deal with __P.
[__STDC__] [!HAVE_CONFIG_H]: Define PTR as in config.h.
[!__STDC__] [!HAVE_CONFIG_H]: Do not undefine static, because
gperf code needs it.
[HAVE_CONFIG_H] [!PTR]: Define PTR (for use with Xemacs).
[HAVE_CONFIG_H] [!__P]: Define __P (for use with Xemacs).
(xmalloc, xrealloc): Use PTR instead of long *.
(bool): Make it a define, not a typedef, for C++ compilers.
(pattern): Members renamed to avoid name clash in some C++ compilers.
(get_language_from_langname): Use const argument.