util: quicker fspath, do not lower names when the length is different

mercurial/util.py

@@ -661,8 +661,9 b' def fspath(name, root):'
         contents = _fspathcache[dir]
 
         lpart = part.lower()
+        lenp = len(part)
         for n in contents:
-            if n.lower() == lpart:
+            if lenp == len(n) and n.lower() == lpart:
                 result.append(n)
                 break
         else: