FIX: Allow isTextBlock to be given a Node or nodeName String

Issue causes Format Block operations to not work with a collpased selection unless the caret is placed in the last half of the block.  Issue appears intermittent at first, but can reproduce it every time cross browser.

 * Fix for issue where isTextBlock would sometimes be given a node object and sometimes given a nodeName
 * Fix for Regular expression to compare case insensitive