RFC: Use editline in winedbg

[Jeremy White]

Hi folks,

The attached patch dynamically detects and uses the BSD licensed editline
library (a pretty close replacement for readline), if it's available.
This gives winedbg command line recall.

This gets around readline's license requirements.

I'm nervous because I wasn't sure if that was the only issue with readline,
or if there were further issues.  Wack me with a clue bat
if this is wrong, otw, I'll submit it.

Cheers,

Jeremy