Blender Git Loki

Text Editor Bugfixes:

The poll() callbacks used in the Text Editor for scrolling and text-
block unlinking operators were too restrictive when the text block was
lib-data.

- Scrolling lib-linked texts is useful for just checking out parts of
the linked-in file that aren't visible on screen already. For example,
checking the specific rig that some UI panels script will work on, or
reading a "README.txt" linked in with notes on which layers various
controls are on. It should be fine that this temporarily modifies the
linked text-block (but for view-settings which will can be reset
later/on file load without any real consequences).
- Unlink operator should be able to be run, otherwise it would be very
difficult to remove linked files from a file (?)