- Back off CMake version requirements.

- Fix plugin extension on OSX (it is .so, not .dylib)
- add SKIP_TESTS to skip compiling test

unittest/libmariadb/CMakeLists.txt

@@ -13,6 +13,10 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 
+IF(SKIP_TESTS)
+  RETURN()
+ENDIF()
+
 ENABLE_TESTING()