Final changes to new build system

[Alan DeKok]

  All of the "non source" directories have been converted to using the
new build system.  This means the directories scripts/, doc/, and raddb/.

  The raddb rules are a bit simpler then the old ones, but depend on GNU
Make specific features.  There's a bit of magic to ensure that existing
config files are never replaced.  But it should work the same as in
previous versions.

  These changes mean that a "make install" is as fast as possible.  Any
changed files are installed, and anything which depends on them.
Everything else isn't rebuilt, and isn't re-installed.

  The new build system is pretty much what I've wanted since FreeRADIUS
was started 14 (!) years ago.  It's simple to use, fast, and clean.

  Thanks to everyone for testing.

  Alan DeKok.