Add an option to specify separator string

This is especially useful in bidi apps, but also when you want to
specify a separator string different from the default "comma-space"
Add Arabic i18n files

Plus corrections to the French main extension file
Identify correctly the files
Merge branch 'master' of github.com:tellibus/jquery-ui-multiselect-widget

# By tellibus
# Via tellibus
* 'master' of github.com:tellibus/jquery-ui-multiselect-widget:
  Identify correctly the files
  Add Arabic i18n files
  Add an option to specify separator string

Conflicts:
	src/jquery.multiselect.js