dire warning regarding wildignore

because I am stupid
allow for .git/tags usage as tpope's commit hook article

in addition to same old .tags/tags stuff
call Setup_Tags after Setup_Completion

Setup_Completion is likely to clobber Setup_Tags, whether called
before or after. But it's more confusing if all looks well from within
Setup_Tags (e.g. with echo tagfiles()) and later does not work
interactively. This positioning lets Setup_Tags visibly fail if
Setup_Completion is wont to wreck it.
actually this is very arbitrary.
deprecate jedi's show_function_definitions->show_call_signatures