Use native, W3C-compliant getAttributeNS() on IE9+

Once again, one of the old IE workarounds broke later IE, once they started doing things correctly.
This commit enables the use of the native, W3C getAttributeNS() on IE9+, fixing tree views, such as
those used in collection composer.

Signed-off-by: Max Fierke <fierk007@umn.edu>