default GUI rfe mode is now Sweep SH
fixed switching between external/internal digitzer not adding auto mode back
added center freq to marker button
disabled CF to marker button when GUI is not in a sweep mode
compare strings with ==
Merge branch 'cf_to_marker'
close device when open/playback dialogs started
enable/disable recording menu options properly
Merge remote-tracking branch 'pyrf/master' into recording

Conflicts:
	pyrf/devices/thinkrf.py