error: make lock inheritance contract violations a subclass of RuntimeError

This is more appropriate, per Pierre-Yves David.

mercurial/error.py

@@ -115,7 +115,7 b' class LockUnavailable(LockError):'
     pass
 
 # LockError is for errors while acquiring the lock -- this is unrelated
-class LockInheritanceContractViolation(AssertionError):
+class LockInheritanceContractViolation(RuntimeError):
     pass
 
 class ResponseError(Exception):