[BUGFIX] RTE: Enable dialogue window resizing in IE

[BUGFIX] RTE: Enable dialogue window resizing in IE

Problem: There was a bug in ExtJS 3.1 that produced a JavaScript
error when a window object was configured as resizable.
Solution: Apparently, this is fixed in ExtJS 3.4, at least in IE and
compatibility modes IE8/IE7.

Change-Id: Icdf93aa61c8b53f4a2a3d4c00db1969cedf2194e
Releases: 4.7, 6.0
Resolves: #38617
Reviewed-on: http://review.typo3.org/12562
Reviewed-by: Stanislas Rolland
Tested-by: Stanislas Rolland