#446 mingw and native x.25 support

[Jay Talbot]

It would be nice to be able to compile under mingw. I have yet to find any documents on compiling xastir under mingw for a stand alone binary.

Also, in it's current x.25 support is Linux only. There cold be an option to include support for OpenAX.25 (http://www.falvotech.com/content/openax25/) functionality as it is cross-platform to at least some degree.