python-wrapper: Fix fixup for wrapped argv[0].

Fixes issues introduced by 24ef871e

.

The problem here is that "import sys; sys.argv[0] = ..." is just
appended after the first "#!", which in turn breaks things such as
encoding specifications. A second problem - although not very common -
is when there's another #! within the script.

This should take care of both cases.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>