This is mostly a simple lexical search+replace but the absence of operator< for
std::weak_ptr<T> leads to some complications, particularly with Evoral::Sequence
and ExportPortChannel.
The class now has two separate methods for setting a duration or a point
value. They MUST be used appropriately, because their behavior is different.
When ::set_duration() is used in timecode mode, an extent (inclusive-end
length) is shown rather than a length.
Some objects, such as the TimeInfoBox, now deliberately shown an inclusive end
for their "end" clock, but this not universally followed, pending more feedback
from users and investigating of conventions in other DAWs.
