Make WAF itself respect OpenBSD shared libraries versioning scheme, too.

Actually, some WAF original code related to shared library handling IS
run in some cases. So patch it to make proper SONAME written in
libraries, which in turn in proper library dependencies in linked
binaries.
Now we have real WANTLIB for Samba4, hooray!

Looks like stuff in ${PREFIX}/lib/samba/ldb/ is some sort of a
plugins collection for LDB, so move it in -main, where they are
actually used. But directory itself, IMHO, should live in -ldb still.
Zap extra directory in -main.
Add a note about installation of public headers to Samba4 TODO.
Oops, remove net/py-dnspython from LIB_DEPENDS-main.
Remove stuff from -main that gone to -talloc, missed before.