Reduce the frequency of dirty calculations in inlineEditor.

inlineEditor no longer calculates the dirty state on every single key
press. Instead, it calculates it at most once every 200ms. This helps to
improve performance when the text field is large.

When it does calculate, the default behavior is now to first compare the
lengths of the strings. If those differ, then there's no need to compare
the string contents.

Reviewed at https://reviews.reviewboard.org/r/6426/
Fix dirty state calculation in inlineEditor.

The recent optimization for inlineEditor resulted in fields that could
not be saved, due to the dirty state not yet being updated.

Now, we force a calculation when we need the value. It will result in an
extra calculation, since a _.throttle can't be canceled, but it
shouldn't have any noticeable impact, as it occurs only on save/cancel
or when specifically requesting the dirty state.

Reviewed at https://reviews.reviewboard.org/r/6433/
Merge branch 'release-0.8.x'