Version bump -> 2.6-SNAPSHOT.
Implement SelectableOption, and use it in place of tuples for select*.
Add an implicit conversion from tuple to SelectableOption.
Refactor, improve readability for SHtml.checkbox[T].
Readability improvements to SHtml.secureOptions[T].
Implement and use SelectableOptionWithNonce during processing.

The SelectableOptionWithNonce class serves as a helper for keeping track
of a SelectableOption's attrs during processing.
Readability improvements to SHtml.secureMultiOptions[T].
Use SelectableOptionWithNonce in secureMultiOptions[T].
Set custom attributes for option tags in select_*.
Fix a MatchError related to the new SelectableOption.
Populate custom option attributes in untrustedSelect_*.
Populate custom option attributes in untrustedMultiSelect_*.
Populate custom option attributes in ajaxUntrustedSelect_*.
Implement SelectableOption support for ajaxSelect*
Make the type bound on SelectableOption* more tolerant.
Clean up some rouge cases.
Oops. Missed a case.
Missed yet another case? Find/replace fails me again.
What will hopefully be the last case-nuking commit.
Add ajaxOnSubmit as an AJAX complement to onSubmit.

This is meant to be applied to a button or input type="submit" element,
and adds the attributes needed to correctly run an AJAX form submission
using that button.