Fix failing DOM test on IE

Note: the `avoidCss3dTransforms` property doesn't have any effect on
browsers that don't css3dtransform.
Default actions is not ignored on input and textareas.
Merge pull request #646 from kevinsimper/fixtouchoninput

Default actions is not ignored on input and textareas.
Prevent _clamp from altering bounds

It's currently possible to specify the viewport bounds, but the _clamp function will overwrite them.

This simply changes how _clamp compares/adjusts the viewport so that the bounds aren't modified.
Merge pull request #642 from potomak/fix-failing-dom-test-on-ie

Fix failing DOM test on IE
Merge pull request #647 from starwed/bound-clamp-fix

Prevent _clamp from altering bounds