Add flag image to immediately after country select.

This flag will automatically update when the selection is changed.

Note: there is also an empty __.gif flag that will show when no selection.
Update patch from HEAD.
Use the COUNTRIES_FLAG_URL setting.
Make the regular expression not require a gif image.
Use the original COUNTRIES_FLAG_URL string for the JS replace.
Merge pull request #59 from schinckel/feature/dynamic-flag-image

Add flag image to immediately after country select.
Make flag_url optional when instanciating a Country object
Don't warn about __.gif transparent flag not matching a country
Fix widget html
Add tests for widget
Don't make CountrySelectWidget the default for now, just document
Fix custom widget, add tests, and don't enable by default for now

Refs #59