Fix #35449: image sequences to drive e.g. particle length or used in modifiers
were no properly updating when rendering animations.

The render engine was only updating the image user current frame on images used
by material textures. Now moved the function that updates all from the editors
to blenkernel level and do it on all frame changes.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56970 954f8c5b-7b00-dc11-b283-0030488c597c