Merge changes from MySQL:

  ChangeSet@1.2645, 2007-12-19 13:24:43+00:00, jperkin@chorlton.adsl.perkin.org.uk +14 -0
    Add new pkgplugindir handling to seperate plugins from libraries,
    and allow override for binary distributions.  Extend mysql_config
    to print compiled-in plugin location for third-party plugins to
    use.  Resolves bug#31736.

and

  ChangeSet@1.2646, 2008-01-02 13:00:46+00:00, jperkin@chorlton.adsl.perkin.org.uk +11 -0
    Use pkglibdir to simplify pkgplugindir, and fix the path in a
    couple of Makefiles.  Continuation of the fix for bug#31736.