Bug 1016184 part 3e - Fix test_reftests_with_caret.html

Turn off the touch caret preference to fix test cases that ought to be
failed by definition of the touch caret behavior.

Thanks Steven Lee <slee@mozilla.com> for the original WIP patch.
Bug 1016184 part 3f - Fix test_paste_selection.html

Synthesize the mouse event at center rather than at (8, 8) since (8, 8)
might be covered by touch caret shown at copy-area.
Bug 1016184 part 3g - Enlarge expiration time in mochitest and reftest
Bug 1016184 part 4 - Enable touch caret by default on b2g