[PATCH] lyxpreview_tools.py: fix a regular expression

[Neven Sajko]

Hmm, after looking at the last few commits, it seems this may be a
more involved issue
than I first thought. On the one hand one has to take care to use the
proper choice
between "Unicode" and "byte" strings, on the other hand it seems like
the Lyx guys want
the script to work for both Python 2 and Python 3.

I'm curious, why is it necessary to support Python 2?

Regards,
Neven Sajko