clone.py:_get_installation_path_from_url() broken on Windows

[mih]

On Debian:

In [2]: _get_installationpath_from_url('/bin/mf/this')                                          
Out[2]: 'this'

On Windows:

(Pdb) print(source)
C:\Users\mih\AppData\Local\Temp\datalad_temp_testrepo_31j9ihq6
(Pdb) _get_installationpath_from_url(source)
'C:\\Users\\mih\\AppData\\Local\\Temp\\datalad_temp_testrepo_31j9ihq6'

which leads to all kinds of follow-up errors, because a clone into the source location is attempted.