Prompt the user for confirmation before removing an export format.

Requested by Radio SRB (http://srb.fm)
Prompt the user for confirmation before removing an export preset

Requested by Radio SRB (http://srb.fm)
remove compilation warning
Merge branch 'patches' of https://github.com/jdekozak/ardour
Merge branch 'radiosrb' of https://github.com/adiknoth/ardour
Merge branch 'master' into meterbridge