Change width calculation of drop-down menu options.

When options are narrower than container set width as usual.
When options are wider than container set width of options to auto.
Bugfix: first key down did not select the first option.
Merge branch 'master' of https://github.com/ilyazub/jquery-selectBox into dev
Fix form submitted automatically in IE on enter
Merge branch 'issue#1' into dev