xfreerdp: smart-sizing and software-gdi fixes

* fixed crash on server-initiated desktop resize and fullscreen toggle with /gdi:sw
* implemented desktop resize for /gdi:sw
* check for availibility of XRender extension and show error messages if a setting would require it
* fixed compile error if xrender devel packages are missing
* fixed bug with server-initiated desktop resize in fullscreen mode
Merge pull request #2246 from nfedera/fix-2014-12-03-01

xfreerdp: smart-sizing and software-gdi fixes