Merge branch 'tc/last-modified-not-a-tree'

Giving "git last-modified" a tree (not a commit-ish) died an uncontrolled death, which has been corrected. * tc/last-modified-not-a-tree: last-modified: verify revision argument is a commit-ish last-modified: remove double error message last-modified: fix memory leak when more than one commit is given last-modified: rewrite error message when more than one commit given