Suggested by Ty Sarna, implemented by me. Useful, because it tells you
how deep you are, and allows you to paste the pathname in to 'cd' to the
directory.
'afterinstall' actually happens *after* the real install!
since this entire section is in a "!target(install)", having
it done the other way was wrong and unnecessary (i.e. the
previous change/comment was bogus).
Use bsd.subdir.mk for building subdirectories.
Don't forget to remove x.cc and x.C when using SHAREDSTRINGS.
Make ${PROG} always depend on ${LIBCRT0}.
Don't duplicate code between cleandir and clean.
Move tags target to bsd.dep.mk.
Move STRIP to bsd.own.mk.
Remove redundant definitions of {BIN,MAN}{DIR,GRP,OWN,MODE}.
Move {LIB,DOC}{DIR,GRP,OWN,MODE} defaults to bsd.own.mk.