Added ismount().

Fixes #661762, bugfix candidate.

Lib/macpath.py

@@ -84,6 +84,11 @@ def splitdrive(p):
 def dirname(s): return split(s)[0]
 def basename(s): return split(s)[1]
 
+def ismount(s):
+	if not isabs(s):
+		return False
+	components = split(s)
+	return len(components) == 2 and components[1] == ''
 
 def isdir(s):
     """Return true if the pathname refers to an existing directory."""