Easy Checks update - Keyboard access to tool-based checks

Added all the keystroke instructions I could see were required for
accessing the IE Web Accessibility Toolbar and the FF Web Developer's
Toolbar for

   - Image Text
Alternatives<http://www.w3.org/WAI/EO/wiki/Web_Accessibility_Preliminary_Evaluation#Image_text_alternatives_.28.22alt_text.22.29>
   - Headings<http://www.w3.org/WAI/EO/wiki/Web_Accessibility_Preliminary_Evaluation#Headings>
   - Forms, form labels, and error
messages<http://www.w3.org/WAI/EO/wiki/Web_Accessibility_Preliminary_Evaluation#Forms.2C_form_labels.2C_and_error_messages>

I also added an alternative instruction for "form labels" in the Forms,
form labels, and error
messages<http://www.w3.org/WAI/EO/wiki/Web_Accessibility_Preliminary_Evaluation#Forms.2C_form_labels.2C_and_error_messages>
 section.

Note - all additions made in the Web Accessibility Preliminary Evaluation
Wiki<http://www.w3.org/WAI/EO/wiki/Web_Accessibility_Preliminary_Evaluation>

Andrew
-- 
Andrew Arch
  Canberra, Australia

“Man does not cease to play because he grows old.
    Man grows old because he ceases to play.”
George Bernard Shaw