fix up meter thread management when JACK client starts/stops/is halted ; put focus...

fix up meter thread management when JACK client starts/stops/is halted ; put focus in plugin search entry when plugin selector is shown ; add WINDOWS_KEY option to gtk2_ardour/SConscript, controlling what X modifier is used for LEVEL4 modifier/bindings ; fix up Keyboard object to properly support LEVEL4 bindings ; fix Playlist::partition_internal() to avoid acting on regions that should not be operated on given the range provided ; fix up more stuff relating to get_regions_for(), including cut/delete ops on edit range vs. regions

git-svn-id: svn://localhost/ardour2/branches/2.0-ongoing@3115 d708f5d6-7413-0410-9779-e7cbd77b26cf