Revert mistaken change: it is UNIX, not Unix.

Revert mistaken change: it is UNIX, not Unix.

        * glib/tmpl/completion.sgml, glib/tmpl/date.sgml,
        glib/tmpl/fileutils.sgml, glib/tmpl/iochannels.sgml,
        glib/tmpl/macros.sgml, glib/tmpl/memory.sgml,
        glib/tmpl/misc_utils.sgml, glib/tmpl/warnings.sgml,
        glib/tmpl/windows.sgml: Revert mistaken change: it is UNIX, not Unix.

        * glib/tmpl/memory_chunks.sgml,
        glib/tmpl/date.sgml, glib/tmpl/threads.sgml,
        glib/tmpl/gtype.sgml: Trivial markup fixes.

        * glib/gconvert.c, glib/giochannel.c, glib/gmain.c,
        glib/gwin32.c: Revert mistaken change: it is UNIX, not Unix.