StGIT cannot import properly from stdin

The import command of stgit does not handle stdin in a very sane way.
The logic expects to be able to read the patch several times which isn't
possible with stdin. So for it to work you have to give it the patch twice.

A simple solution would be to store it to disk and then handle it the
same way as if a file had been given on the command line.

Rgds
Pierre