[issue52] adding support for long path names on Windows

Hi,

Two Co-workers and I created a patch, which enables msysgit
to handle long path names. 

We consider the patch as "proposal" and want to get some feedback.
Applying the patch to v.1.8.3 will pass every integration test,
which un-patched version also does.

AFAIK, these things are still to do:
 * writing a test
 * split xutftowcs_path into separate functions for character
   conversion and prefixing - so de-prefixing can be avoided
   at some places
 * checking upper array boundaries

Please, give this patch a try and send feedback.

Thanks 
Andi, Eric, Martin