SciTE tabs.
This does not allow primary selection to work between tabs as the tabs are
sharing a single Scintilla and the old primary selection is unclaimed when the
file is changed.
This fix adds a new ReceivedClipboard method which does not try to convert the
selection if received in a different format than asked for. It was the call to
gtk_selection_convert that seemed to cause the flickering. ReceivedClipboard is
only called from SelectionReceiver::ClipboardReceived so only occurs due to a
call to RequestSelection and can not occur because of a selection_received
signal.
ReceivedSelection is left with its complexity in case it is needed for some
other issue although it doesn't appear to be called for drag&drop, for example.

accessibility if UTF32 index not available.

This allows the accessibility layer to request detail, such as which
characters have been deleted.  ATK will query the deleted range to
report the data that was removed, so it must still be available for
the query to give a correct answer.
So, emit the signal in BEFOREDELETE instead of DELETETEXT.

It's quite a lot faster even after trying and optimizing the custom
version, and it makes the code simpler.

Also improve ByteOffsetFromCharacterOffset() to make use of the cache,
making it drastically faster.

implementation.

Dependencies files deps.mak and nmdeps.mak are formatted with one file per line
as that makes it easier to examine differences between versions.

be needed for adding a CharacterCategory feature.