refine bestrelpath to return "." for X.bestrelpath(X) and refine its docstring

--HG--
branch : trunk

CHANGELOG

@@ -53,6 +53,8 @@ Bug fixes / Maintenance
   on all python versions
 - install plain py.test/py.which scripts also for Jython, this helps to
   get canonical script paths in virtualenv situations
+- make path.bestrelpath(path) return ".", note that when calling 
+  X.bestrelpath the assumption is that X is a directory. 
 
 Changes between 1.3.0 and 1.3.1
 ==================================================

py/_path/common.py

@@ -194,10 +194,13 @@ newline will be removed from the end of each line. """
 
     def bestrelpath(self, dest): 
         """ return a string which is a relative path from self 
-            to dest such that self.join(bestrelpath) == dest and 
+            (assumed to be a directory) to dest such that 
-            if not such path can be determined return dest. 
+            self.join(bestrelpath) == dest and if not such 
+            path can be determined return dest. 
         """ 
         try:
+            if self == dest:
+                return os.curdir
             base = self.common(dest)
             if not base:  # can be the case on windows
                 return str(dest)
@@ -207,7 +210,7 @@ newline will be removed from the end of each line. """
                 n = self2base.count(self.sep) + 1
             else:
                 n = 0
-            l = ['..'] * n
+            l = [os.pardir] * n
             if reldest:
                 l.append(reldest)     
             target = dest.sep.join(l)

testing/path/common.py

@@ -117,6 +117,8 @@ class CommonFSTests(object):
     def test_bestrelpath(self, path1):
         curdir = path1
         sep = curdir.sep
+        s = curdir.bestrelpath(curdir)
+        assert s == "."
         s = curdir.bestrelpath(curdir.join("hello", "world"))
         assert s == "hello" + sep + "world"