actually do something in WaveView::region_resized() which is called whenever the region is resized; implement WaveView::set_region_start() which could be used by an xfade editor etc.
fix the naming and behavior of always-play-range to match the button, which is follow-edits.  when you select a range, the playhead should jump to the start of the range and begin to play the selection.  BUT (unlike previous implementation) if the user wants to relocate the playhead, then that should be allowed.  The user should always remain in charge of the playhead location.  NOTE:  your previous config setting will be invalidated.  You must re-save a session to overwrite with the new config variable
if a Range end is trimmed, in follow-edits mode, locate to the range end so it can be auditioned.  (same as trimming a region end)
revert part of 0f1c7b1d7107 which broke lots of stuff based on region selection
lots of keybinding changes.  added a new action to allow removing markers at the playhead location.  numpad now allows you to access marks higher than 9.  to locate to a marker, use the numpad decimal to start and end the operation - for example press .19. to locate to marker 19.   also added alternate bindings for redo, delete, and several other alternates that will be needed in subsequent commits.   tab is not working, using either Tab or nabla in the binding.in file
add new regions created by split to selection after operation is complete
remove all accelerator declarations from ardour.menus.in, since they are about to be automatically registered for ALL actions
add ActionManager::enable_accelerators(), which takes all known Actions and registers them via the UIManager as accelerators.

This makes them available for use with key bindings/shortcuts/accelerators even if they have no proxy widget
move location of menus file loading and call ActionManager::enable_accelerators() to get all actions setup for binding options
rename the action that cycles through edit modes, since there are more than two
disable latency-compensation preparations for now

Don't add delaylines to tracks by default just yet,
currently only sends are aligned with delaylines
fix up various keybindings added/modified by Ben so that they work.

There is still the mystery of why we can specify Return and KP_Return but not Tab.
purge states of Audio-backends that are N/A

fixes crashes/assert() when using different builds while
sharing ardour.rc with n/a engine backends marked active.
debug info to trace down "cannot rename temp session file" errors

..but actually, the real error may be concurrent
calls to Session::save_state()
Merge branch 'cairocanvas' into recfolder