gdb.texinfo: advance manual revision dates to present
gdbinv-s.texi, gdb.texinfo, all-config.texi, h8-config.texi:
stop using silly Roman numerals in @set variable names
(the usual) non-specialized versions of the manual.
gdb.texinfo: list of nonstandard init file names, with brief descriptions
(permits closing PRMS gdb/2296).
(a) to make H8 configuration come out right (first attempt since
conversion to texinfo conditionals);
(b) to exploit yesterday's makeinfo bugfix, using conditionals in menus
rather than multiple alternative menus.
2. Update H8 text to refer to H8/500 as well as H8/300.
3. Define config file gdb-config.texi as a link in Makefile, based on a
DOC_CONFIG variable.
