Delete minus1Trunc.v, close #434
easy lemma `issurj` for defining surjections
change equiv_tr to tr
isequiv_surj_emb
BuildIsSurjection
check for truncatedness of the goal in strip_truncations
Merge pull request #513 from mikeshulman/minus1trunc

Delete minus1Trunc.v, close #434
./autogen.sh