[Gpsbabel-code] Really stupid patch to gpx.c

[Ron P. <ro...@pa...>]

Why "really stupid?"  Because we shouldn't have to do it.

However, in case Robert feels it would be worthwhile, I
have written a little patch to gpx.c that tries to find
strings of the form � through  and eliminate
them from the input stream before Expat gets them.  It's
probably not perfect - some such sequences can overlap
the boundary between reads, and I only mostly handle that
situation - but it does make GPSBabel successfully read
at least three of my files that are infected with
Groundspeak-itis (a condition characterized by odd growths
of nonprinting characters on the end of log text.)

So, what do y'all say?  Should we put pragmatism before
perfection, as we did with the stupid EasyGPS parser bug?
Should I check this mess in?