Added html5data methods set/get

Based on the issue below sethtml5data() and gethtml5data() will write to
the dataset and the write the data-* attributes correctly in any
browsers that Prototype supports.

https://prototype.lighthouseapp.com/projects/8886/tickets/250-support-for-dataset-property-and-data-attributes
code optimizations suggested by @victor-homyakov
missing curly brace caused error
curly brace styling
Fix for IE10 readattribute test

https://prototype.lighthouseapp.com/projects/8886-prototype/tickets/1631-expected-identifier-error-on-page-load-in-ie-10
wrapped setAttribute in try/catch to satisfy IE10

IE10 is not expecting a raw function as an attribute value so this wraps the attempt to set the value to a raw function in a try catch block

tested on IE6, 7, 8, 9, 10 beta using IETester
tested on latest Chrome and latest Firefox
missed paren

grr github editor doesnt respond fast enough
Merge remote-tracking branch 'origin/IE10-Attr-Test'