Absolutise all typemaps because with deep-located typemaps, eg
"lib/XS/typemap", if xsubpp is called from top level with
    $(XSUBPP) ... -typemap "lib/XS/typemap" "lib/XS/Test.xs"
it says:
    Can't find lib/XS/type map in (fulldir)/lib/XS
because ExtUtils::ParseXS::process_file chdir's to .xs file's
location. This is the only way to get all specified typemaps used,
wherever located.
Sort realclean files = diff-able Makefiles
RE with interpolated filename needs quotemeta
xs_obj_opt method adds -o to all $(CCCMD) commands to put .o next to .c
Eliminate && from Makefile recipes - totally unnecessary