python-wrapper: Fix handling of line breaks.

Not really critical for anything we have in <nixpkgs> I guess, but
skipping lines three times really was a workaround and we're better off
just appending the lines ending with backslash to the pattern space so
we can accumulate all the crap until the last line of crap (crap, that
is "broken lines").

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