Extend External Passage list support.
* Allow manual refreshing of list.
* Allow TWS files referenced in StoryIncludes to also contain a
StoryIncludes passage.
* Allow suppressing of list refreshing on startup.
Merge pull request #148 from greyelf/child_story_includes

Support resolving of external passage links in child .tws files
1.4.2 post-release bugfixes

* Fixed a bug where macros.remember.prefix would always be set to
"Twine.undefined.". Now, it's set to "Twine." plus the default name of
the story (as compared to the StoryTitle name).
* Fixed a bug where the 'cancel' button on offerAssistance dialogs would
still cause the passage to be closed.
* Altered the name of the "Refresh Includes Links" menu item to "Update
StoryIncludes Links". Also, this menu item will be disabled if
StoryIncludes isn't present.
* Now, closing StorySettings will refresh the StoryIncludes links
automatically.
* Fixed a bug where the returned Wikifier.linkFunction would still call
state.display() even when no title was passed (e.g. if a custom macro
created an internal link which, of course, would have this as an event
listener).
* Removed the History.prototype.display startup check, on the basis that
its use-case is a bit too obscure.
* Changed version number to 1.4.3.
Richard Lake
Changed how storypanel.py keeps track of widgets from a list to a dict keyed on their title.
This is in order to speed up getConnectedWidgets which is used to paint widgets. The linear scan through a list was using a unreasonable amount of time in stories with large numbers of widgets.
 On a test story with ~800 passages this went from 13.7  to 0.137 milli-seconds per call.
Richard Lake
Slightly speed up lineIntersection.
Speed up lineRectIntersection with Cohen–Sutherland algorithm instead of testing against all four lines
 ~4 times faster on my machine
Richard Lake
Speed up lineRectIntersection with Cohen–Sutherland algorithm instead of testing against all four lines
 ~4 times faster on my machine
Richard Lake
Fixed the tweaking on the connector lines to not break at higher zoom levels.
Richard Lake
Merge remote-tracking branch 'origin/master'

Conflicts:
	storypanel.py