Add test case for segfault-on-emu_stop() bug.

The following code segfaults:
unicorn.Uc(unicorn.UC_ARCH_X86, unicorn.UC_MODE_64).emu_stop()

Tested under Linux and OS X.

tests/regress/segfault_on_stop.py

@@ -0,0 +1,13 @@
+#!/usr/bin/env python
+
+import regress
+import unicorn
+
+
+class SegfaultOnStop(regress.RegressTest):
+    def test(self):
+        unicorn.Uc(unicorn.UC_ARCH_X86, unicorn.UC_MODE_64).emu_stop()
+        self.assertTrue(True, "If not reached, then we have a crashing bug.")
+
+if __name__ == '__main__':
+    regress.main()