kernel: Sync resource_string_value() with FreeBSD
makewhatis: scan for potentially missing MLINKS in verbose mode

Since makewhatis has been switched to tracking files only, it's
likely that a couple of names specified in the manual pages can't
be found anymore.  In order to spot which are missing, verbose
mode now prints likely candidates for MLINKS.

While there, plug the strdup() leaks by erroring out properly,
and reduce the diff against the unmodified version.
cacos.3: add missing commas
kernel: Remove useless get/rel_mplock() sequence
libc/sys: Fix Makefile typo.
libc/gen: Remove 0 byte long msg*.3 files.
rc: Put back the sysvipc line. Some more adjustment is needed here.