[krbdev.mit.edu #1806] should default to shared libraries in future

[Ken Raeburn via RT]

We should probably switch the default to be to build shared libraries
on most if not all platforms.  Static libraries should still be
buildable, but my guess is we shouldn't bother by default.

However, this does imply that we should try to fix some of the
problems relating to testing programs linked against uninstalled
shared libraries.

Ken