groupConnectivity.pyx: add signal handling

groupConnectivity.pyx

+include "cysignals/signals.pxi"
+
 from libcpp.vector cimport vector
 from libcpp cimport bool
 from libcpp.utility cimport pair
@@ -138,7 +140,9 @@ def testGroupConnectivity(G, group = "Z4", getClasses = False,
     print "Double subdivided edges: ", doubleSubdivisions
 
   tester.init(G.num_edges(), spanningTreeEdges, twoCuts, doubleSubdivisions, elemCycles)
+  sig_on()
   ret = tester.run()
+  sig_off()
 
   if getClasses:
     classes = tester.getClasses()