ExportHelper: Always clean up the export operators, even if the user cancelled the export.
Fixes ilastik-579.
File Export widget: Changed error text to be more general (errors could be from more than just the shape)
ShortcutManager: Catch KeyError in case where multiple shortcuts have the same keyseq.
tiling: When an exception is caught in the layer-rendering thread, print the layer name (if possible).
de-register callback; no effect on ilastik bug 575 though
clip painting of capped-lines (brush strokes) to data rect
Layer, datasouces changes:
- datasources: Provide numberOfChannels property and numberOfChannelsChanged signal.
- layer: Provide datasources list as constructor arg in Layer base class.
- layer: Update numberOfChannels if the underlying datasource channels changes.
Fixes ilastik/ilastik#443
tests: Updated test code for change to Layer.__init__ params.