This is required when adding locked regions to a playlist.
e.g. after a split or partition operation. It is only supposed
to be used from Playlist::add_region_internal() and
Playlist::partition_internal().
This allows to copy a property list and then selectively
replace various properties. e.g.
```
PropertyList plist (region->properties ());
plist.add (Properties::length, len);
plist.remove (Properties::start);
```
See also 8b0ab38675
and 97f0fac7d5
This also fixes the issue referenced in
8c83149c4c
Before, the .cue file could end up with a mix of latin1 and utf-8
encodings. Utf-8 works better for many things, but that doesn't matter
when the .cue file has to be in latin-1.
Play loop, change loop-location, undo.
Undo calls Locations::set_state, takes a writer-lock,
and calls Location::set_state which emits a Changed signal.
This triggers Editor::location_changed, and if loop-location
changed while looping, update_loop_range_view() queries the
loop location, taking a reader-lock.
This leads to a recursive lock, RWLock::ReaderLock after
a RWLock::WriterLock does not cause a deadlock, however
releasing the ReaderLock effectively also unlocks the WriterLock.
This leads to a deadlock next time a writer-lock is acquired.
Sadly some popular Window Managers do not follow
freedesktop.org specifications. This results in Ardour's splash
screen obscuring session setup dialogs on those systems.
'unbang' is better described as a mouse-up or button-release event
* if launch-style is Gate or Repeat, then UnBang will stop the playing clip
* in other launch-styles, UnBang is ignored
some prior code using UnBang will change to
stop_quantized() or request_stop()
Grid controllers will largely want to access clips in the order they appear on the Cue page
It is up to the device (and/or its ControlProtocol) to handle banking
normally we operate on TriggerPtr's which are a safe way to track
trigger lifetime, safely modify their properties, and launch them.
bang_trigger_at() is a convenience function to look up a trigger by index,
and launch it, in one step. Potentially useful for control surfaces.
