- Simplify sql-bench installation, 
do not try to resolve names : this leads to probem
if builddir is symlink located on different filesystem.
(reported by alik)

- Make WITHOUT_XXX (disabling plugin) work for DEFAULT
plugins. Prior to the patch is behaved just like 
MANDATORY.

- LINK_LIBRARIES in MYSQL_ADD_PLUGIN had no effect for
statically linked plugins.

- Fix constant rebuild of initdb target on Windows.