Add ENABLE_PYTHON3 to the conditional that triggers building bindings

ENABLE_PYTHON3 is used in the CMakeLists.txt in the bindings
directory but if it's defined alone it won't trigger building the
bindings.

Author: dralley

CMakeLists.txt

@@ -431,9 +431,9 @@ ENDIF (HAVE_LINKER_AS_NEEDED)
 ADD_SUBDIRECTORY (src)
 ADD_SUBDIRECTORY (ext)
 ADD_SUBDIRECTORY (tools)
-IF (ENABLE_PERL OR ENABLE_PYTHON OR ENABLE_RUBY OR ENABLE_TCL)
+IF (ENABLE_PERL OR ENABLE_PYTHON OR ENABLE_PYTHON3 OR ENABLE_RUBY OR ENABLE_TCL)
     ADD_SUBDIRECTORY (bindings)
-ENDIF (ENABLE_PERL OR ENABLE_PYTHON OR ENABLE_RUBY OR ENABLE_TCL)
+ENDIF (ENABLE_PERL OR ENABLE_PYTHON OR ENABLE_PYTHON3 OR ENABLE_RUBY OR ENABLE_TCL)
 ADD_SUBDIRECTORY (examples)
 ADD_SUBDIRECTORY (doc)