Additional checks for PROG/mkc.prog.mk, LIB/mkc.lib.mk etc.
set -x was removed from mkc.mk
mkc_imp.init.mk renamed to mkc.init.mk
mkc.sub{dir,prj}.mk: dash is not allowed inside subdir
Regression test for mk files vs. PROG/LIB/SUBDIR/SUBPRJ checks
TODO: -1 task (NetBSD mkdep(1))
TODO: clean-ups