Use SC.browser.version instead of SC.browser.engineVersion for IE.

The SC.browser.engineVersion will be equal to SC.browser.version for some
versions of IE, but that should not be relied on, as some versions
correctly set SC.browser.engineVersion to the Trident version.
Merge pull request #1119 from sproutcore/team/fairbanksg/ie11-engineVersion

Use SC.browser.version instead of SC.browser.engineVersion for IE.