Raise an human readable exception if an unversioned directory exists.

gclient.py

Index: gclient.py
===================================================================
--- gclient.py	(revision 16052)
+++ gclient.py	(working copy)
@@ -788,6 +788,10 @@
 
     # Get the existing scm url and the revision number of the current checkout.
     from_info = CaptureSVNInfo(os.path.join(checkout_path, '.'), '.')
+    if not from_info:
+      raise Error("Can't update/checkout %s if an unversioned directory is "

[sgk, 2009/05/15 05:18:29]

Nit:  I prefer %r in messages like this so the string is quoted.  The error
message is more readable if something weird happens and the value is a null
string.

+                  "present. Delete the directory and try again." %
+                  checkout_path)
 
     if options.manually_grab_svn_rev:
       # Retrieve the current HEAD version because svn is slow at null updates.