Code clean-ups.
mkc.init.mk visible to users should not contain suffix rules, only variables.
NOSUBDIR also affects NODEPS and dependency graph
mkc.subprj.mk: new target "print-deps" was introduced.
mk-configure.7: targets specific to mkc.subprj.mk are described in appropriate section.
Update TODO
Remove useless REC_MAKEFILES from EXPORT_VARNAMES