Bugfix: "Change Frame" operator for setting current frame by clicking/scrubbing
in a timeline view would show up search results in other editors (e.g. 3D View).

This only really works where there is a timeline view as:
1) The modal interactive stuff is built on the assumption that a suitable 2D
view mapping exists
2) The operator is not "registered" (i.e. no props display after usage, and
doesn't get shown in undo) as it's more "view state" than "scene data"

Rewrote poll callback to handlethis properly


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@53582 954f8c5b-7b00-dc11-b283-0030488c597c