Update Forall.v

Variation on dpath_forall
Fiddling.

Signed-off-by: jcmckeown <jesse@sockwright>
Merge branch 'master' of https://github.com/jcmckeown/HoTT
Getting sections closed correctly
Better description of dsigma_forall'
Merge branch 'master' of github.com:HoTT/HoTT