Log Message:
Update to patch release 21.4.24. From the ChangeLog:

2015-03-24 Vin Shelton <acs@xemacs.org>

        * XEmacs 21.4.24 is released

2015-02-23  Vin Shelton  <acs@xemacs.org>

        * configure.in: Add LIBOSSAUDIO as appropriate.  Patch from netbsd
        via Hauke Fath.
        * configure: Rebuild.

2015-02-15  Vin Shelton  <acs@xemacs.org>

        * configure.in: Additional netbsd platform definitions.
        * configure: Rebuild.

I have used the opportunity for a bit of spring cleaning:

o remove build restrictions for powerpc and mips (hacks.mk, Makefile)
o drop the inactive X11 toolkit options - they were never used, and
  upstream does not support them for 21.4, anyway (options.mk)
o add comments to patch files
o upstream converted the texinfo files to v5 format. Patch the offenders
  to be v4 compatible