subprocesses catch keyboardinterrupt and raise a proper exception.

This causes the parent process to re-raise the exception when it
eventually tries to get() the result from the child, instead of hanging
forever on a ctrl-C. It doesn't happen immediately, which is not ideal,
but at least things will eventually exit on ctrl-C now.

chunk.py

@@ -52,6 +52,14 @@ def render_and_save(chunkfile, cave=False):
         import traceback
         traceback.print_exc()
         raise
+    except KeyboardInterrupt:
+        print
+        print "You pressed Ctrl-C. Unfortunately it got caught by a subprocess"
+        print "The program will terminate... eventually, but the main process"
+        print "may take a while to realize something went wrong."
+        print "To exit immediately, you'll need to kill this process some other"
+        print "way"
+        raise Exception()
 
 class ChunkRenderer(object):
     def __init__(self, chunkfile):