add small check for swig

Author: gridley

setup.py

@@ -2,7 +2,7 @@
 The setup script for OpenMOC
 '''
 
-import os, site, string, sys
+import os, shutil, site, string, sys
 from distutils.errors import DistutilsOptionError
 import distutils.ccompiler
 import multiprocessing
@@ -114,6 +114,12 @@ def initialize_options(self):
     self.coverage_mode = False
     self.with_ccache = False
 
+    # Check that swig is installed:
+    swigLocation = shutil.which('swig')
+    if not swigLocation:
+        print("-> Please install swig before building <-")
+        sys.exit()
+
 
   def finalize_options(self):
     """Extract options from the flags invoked by the user at compile time.