[BUGFIX] In IE9, RTE does not work correctly in compat modes IE8/IE7

[BUGFIX] In IE9, RTE does not work correctly in compat modes IE8/IE7

Problem: When using IE9, the RTE does not work correctly when using
compatibility modes IE8 or IE7. In particular, the style sheets are not
parsed, because they are not loaded in the same order as with the
specified compatibility version.
Solution: Check whether compatibility mode is activated and avoid
reliance on order.

Change-Id: I7a1ecf4ad0a4343311ce5aea4edcb893c58750e4
Releases: 4.5, 4.6, 4.7, 6.0
Resolves: #38574
Reviewed-on: http://review.typo3.org/12560
Reviewed-by: Stanislas Rolland
Tested-by: Stanislas Rolland