Document effect of preventDefault on touchend event

After this Gecko bug is fixed, canceling a "touchend" event will prevent 
that touch from generating a click event and associated mouse events:
https://bugzilla.mozilla.org/show_bug.cgi?id=1016481

The new Gecko behavior matches the current behavior of Chrome and WebKit.

The Touch Events v1 recommendation does not explicitly document this 
behavior, though it is perhaps implied by the table in section 5.4. To 
make it fully explicit, I suggest adding this text to section 5.6 ("The 
touchend event") in the errata:

"*If this event is cancelled, any sequence of touch events that includes 
this event must not be interpreted as a click [link to section 7].*"

and the following text (inserted text in bold below) to section 7:

"If the preventDefault method of touchstart or touchmove*or touchend* is 
called, the user agent should not dispatch any mouse event that would be 
a consequential result of the the prevented touch event."