Updating SWIG to a patched version

The superbuild swig has been repackages with the additional commit for
SWIG upstream: 843aa7cd65985319a64d4f1297778f93f96a5008 to address
compilation issue on OSX Maverics.

Change-Id: Ia155dcb35f940148e3759818d06055056374865a
Merge topic 'SIMPLEITK-496_FixJavaVectorBoolWithC++11' into next

2642ae21 Updating SWIG to a patched version