Don't setInputData unless value changed

When using a text input rather than textarea, updating the value moves
the cursor to the end of the line. Since core triggers setInputData on
every keystroke, this makes it impossible to highlight, copy, paste, or
move the cursor within the text.

Fix by only updating the value if it has changed.

I believe this also fixes the following known issue:
http://github.com/alexgorbatchev/jquery-textext/issues/50
Merge branch 'master' of https://github.com/causes/jquery-textext