when Session emits RouteAdded, each handler (editor, mixer, trigger pages etc) will
execute their callbacks in order. But Editor::add_routes() selects the routes too,
which triggers a PresentationInfo::Change signal. This is received by e.g. the Mixer
before it has even found out about the newly added stripables. This in turn
leads to severe confusion regarding the state of the selection in the mixer,
and potentially elsewhere.
So, just add a PresentationInfo::ChangeSuspender for the scope of the RouteAdde
signal emission
Initially thew new region has a length of zero (0:0). When
merging Notes from a truncated region (no explicit note-off)
those notes are lost:
"Stuck note resolution - end time @ 0:0 is before note on: @ 0:0"
Truncate (or split) a region so that a note is cut short:
```
Region [{<--Note-------->}]
```
becomes
```
Region [{<--Note--]
^ implicit note-off at region boundary
```
When combining this region with an empty Region after gap,
```
Region [{<--Note--] [ ]
```
the result should be
```
Region [{<--Note->} ]
```
For this reason, even without a gap between the regions,
the original note length must not be restored.
The result MUST NOT be the same as the original:
```
Region [{<--Note-------->}]
```
Playlist::split can result in removal of a region
(adding two others instead). In this case the state
of the removed region (if modified) is not saved.
I/O plugin Controls are destroyed with ~IOPlug, however
Session::destroy()'s call to drop_references() still
triggers AutomationControl::session_going_away() on the
binding proxy.
This is even properly documented in session_object.h:
> A named object associated with a Session. Objects derived
> from this class are expected to be destroyed before the
> session calls drop_references().
Playlist::add_region, Playlist::add_region_internal always
adds the region to the top of the playlist, ignoring the
region's layer.
Note that there is also difference between
Region::layer and Region::layering_index.
Previously creating a new preset first attempted to load
it from disk, before creating it. This resulted in a
`XML error: failed to load external entity`.
