Fix UIExpandingTextView::set{Minimum,Maximum}NumberOfLines breaking input method context.

When UIExpandingTextVIew’s height changes, setMaximumNumberOfLines is called. The method always changes text property temporarily and restores it; therefore breaking input method context in some languages (e.g. Korean). This commit prevents it by only doing things when the value is actually changed. It’s not a perfect solution, but it will work in most cases.
Merge pull request #122 from dittos/master

Fix broken input method context when UIExpandingTextView's height changed