Bugfix [#35668] Tooltip for Euler Discontinuity Filter was misleading

The tooltip seemed to hint that this tool is able to resolve all manner of
gimble-lock situations by untangling the curves (i.e. performing some kind of
equivalent-angles resolution, keeping in mind the nearest situations nearby).
However, this tool currently only performs corrections for the most basic case
when large jump+flip discontinuity artifacts appear in euler rotation curves as
a result of rotation values getting clipped to +/- 180 degrees, which arises
when these rotation curves are the result of baking some physics sim or so.

(Also, fixed an unrelated "replace-all" typo in a comment)


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57411 954f8c5b-7b00-dc11-b283-0030488c597c
Cleaned code a bit around 2D stabilization

Hopefully it's more readable now. Took me a while to remmeber
all the stuff going on here while was looking into possibility
of implementing some feature here.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57412 954f8c5b-7b00-dc11-b283-0030488c597c