Added jQuery 1.9.0 to project

Updated demo and test index.html's as well as test include so it
defaults to latest jQuery: 1.9.0
Fixed error in test case

"validating multiple checkboxes with 'required'". attr() set is now
deprecated in jQuery 1.9.0. Changed it to prop instead.
Changed $.fn.attr() to $.fn.prop() where possible

No longer supports jQuery <1.6. Doesn't break any tests, but change any
other use of attr() and a test breaks.
Enforced types in rules module

Changed tests and Validate to adapt to prop() which uses real types.
I.e. a number cannot be saved as a string, just like with prop().
Updated .showLabel to use prop()

Changed attr() usage to prop() usage in .showLabel(), to better work
with jQuery 1.9.
Added comment to new method

Added a comment to explain the new method attrConv(). It should probably
be hidden though. It's just there to make
Fixed test parameter order in test.js

Expected and Result were in the wrong order for about half the tests in
test.js. Fixed.