shelve: move commitfunc creation to a separate function
Special commitfuncs are created as closures at least twice in shelve's
code and one time special commitfunc is used within another closure.
They all serve very specific purposes like temporarily tweak some
configuration or enable editor, etc. This is not immediately important
to someone reading shelve code, so I think moving this logic to a separate
function is a good idea.
Test issue2761
$ hg init
$ touch to-be-deleted
$ hg add
adding to-be-deleted
$ hg ci -m first
$ echo a > to-be-deleted
$ hg ci -m second
$ rm to-be-deleted
$ hg diff -r 0
Same issue, different code path
$ hg up -C
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ touch does-not-exist-in-1
$ hg add
adding does-not-exist-in-1
$ hg ci -m third
$ rm does-not-exist-in-1
$ hg diff -r 1