copies: return True instead of filename as it is expected to return boolean

As the function documentation says this function should True if we hit
a match and False otherwise. And I see that we are not using that returned
filename anywhere.

Differential Revision: https://phab.mercurial-scm.org/D5964

mercurial/copies.py

@@ -776,7 +776,7 b' def _related(f1, f2):'
     """
 
     if f1 == f2:
-        return f1 # a match
+        return True # a match
 
     g1, g2 = f1.ancestors(), f2.ancestors()
     try: