[FEATURE] RTE: Always use standards-based methods in IE9 native-mode

[FEATURE] RTE: Always use standards-based methods in IE9 native-mode

Description: When IE9 is used in native IE9 mode, the RTE should
always use the standards-based methods supported by IE9.

Change-Id: I1a4b94706600c559e8468684441e6034089c16ba
Releases: 6.0
Resolves: #38656
Reviewed-on: http://review.typo3.org/12616
Reviewed-by: Stanislas Rolland
Tested-by: Stanislas Rolland