glossary: more precise definition of tree-ish (a.k.a. treeish)
glossary: more precise definition of tree-ish (a.k.a. treeish)

A tree-ish isn't a ref.  Also, mention dereferencing, and that a
commit dereferences to a tree, to support gitrevisions(7) and
rev-parse's error messages.

Signed-off-by: Richard Hansen <b2eb39c2540dc27c75dc44a8dc9f96af73df0e80@bbn.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git