move util.Abort to error.py

mercurial/error.py

@@ -62,3 +62,6 b' class SignalInterrupt(KeyboardInterrupt)'
 
 class SignatureError(Exception):
     pass
+
+class Abort(Exception):
+    """Raised if a command needs to print an error and exit."""

mercurial/util.py

@@ -333,8 +333,7 b' def increasingchunks(source, min=1024, m'
     if buf:
         yield ''.join(buf)
 
-class Abort(Exception):
-    """Raised if a command needs to print an error and exit."""
+Abort = error.Abort
 
 def always(fn): return True
 def never(fn): return False