worker: handle interrupt on windows

After applying suggestions from https://phab.mercurial-scm.org/D1564
to catch all exceptions in the same way I actually broke the handling of
KeyboardInterrupt on windows. The reason is that KeyboardInterrupt doesn't
dervie from Exception, but BaseException:
https://docs.python.org/2/library/exceptions.html starting from python 2.5

Test Plan:
Run hg on windows and ctrl-c during a large update. No random
exceptions from threads surface in the shell. Previously we'd nearly always get
stack traces from some of threads

Run tests ./run-tests.py
[...]
Failed test-convert-svn-encoding.t: output changed
# Ran 622 tests, 41 skipped, 1 failed.
python hash seed: 2962682116

The test failing seems to have nothing to do with the change and fails on base
revision as well

Differential Revision: https://phab.mercurial-scm.org/D1718

mercurial/worker.py

@@ -282,7 +282,7 b' def _windowsworker(ui, func, staticargs,'
                 if t.exception is not None:
                     raise t.exception
                 threads.remove(t)
-    except Exception: # re-raises
+    except (Exception, KeyboardInterrupt): # re-raises
         trykillworkers()
         raise
     while not resultqueue.empty():