errors: make StorageError subclass Error, attaching an exit code to it

Differential Revision: https://phab.mercurial-scm.org/D10741

mercurial/error.py

@@ -91,13 +91,16 b' class Abort(Error):'
     """Raised if a command needs to print an error and exit."""
 
 
-class StorageError(Hint, Exception):
+class StorageError(Error):
     """Raised when an error occurs in a storage layer.
 
     Usually subclassed by a storage-specific exception.
     """
 
-    __bytes__ = _tobytes
+    def __init__(self, message, hint=None):
+        super(StorageError, self).__init__(
+            message, hint=hint, detailed_exit_code=50
+        )
 
 
 class RevlogError(StorageError):

mercurial/scmutil.py

@@ -198,11 +198,6 b' def callcatch(ui, func):'
             ui.error(b"\n%r\n" % pycompat.bytestr(stringutil.ellipsis(msg)))
     except error.CensoredNodeError as inst:
         ui.error(_(b"abort: file censored %s\n") % inst)
-    except error.StorageError as inst:
-        ui.error(_(b"abort: %s\n") % inst)
-        if inst.hint:
-            ui.error(_(b"(%s)\n") % inst.hint)
-        detailed_exit_code = 50
     except error.WdirUnsupported:
         ui.error(_(b"abort: working directory revision cannot be specified\n"))
     except error.Error as inst: