Re: [PATCH 8/7] mergetool--lib: don't call "exit" in setup_tool

Applying this one on top of 1/7 thru 5/7 and 7/7 seems to break
t7610 rather badly.

--- >8 ------ >8 ------ >8 ------ >8 ------ >8 ------ >8 ---

...
ok 1 - setup

expecting success:
    git checkout -b test1 branch1 &&
    git submodule update -N &&
    test_must_fail git merge master >/dev/null 2>&1 &&
    ( yes "" | git mergetool both >/dev/null 2>&1 ) &&
    ( yes "" | git mergetool file1 file1 ) &&
    ( yes "" | git mergetool file2 "spaced name" >/dev/null 2>&1 ) &&
    ( yes "" | git mergetool subdir/file3 >/dev/null 2>&1 ) &&
    ( yes "d" | git mergetool file11 >/dev/null 2>&1 ) &&
    ( yes "d" | git mergetool file12 >/dev/null 2>&1 ) &&
    ( yes "l" | git mergetool submod >/dev/null 2>&1 ) &&
    test "$(cat file1)" = "master updated" &&
    test "$(cat file2)" = "master new" &&
    test "$(cat subdir/file3)" = "master new sub" &&
    test "$(cat submod/bar)" = "branch1 submodule" &&
    git commit -m "branch1 resolved with mergetool"

M       submod
Switched to a new branch 'test1'
Submodule path 'submod': checked out '39c7f044ed2e6a9cebd5266529badd181c8762b5'
not ok - 2 custom mergetool
#
#           git checkout -b test1 branch1 &&
#           git submodule update -N &&
#           test_must_fail git merge master >/dev/null 2>&1 &&
#           ( yes "" | git mergetool both >/dev/null 2>&1 ) &&
#           ( yes "" | git mergetool file1 file1 ) &&
#           ( yes "" | git mergetool file2 "spaced name" >/dev/null 2>&1 ) &&
#           ( yes "" | git mergetool subdir/file3 >/dev/null 2>&1 ) &&
#           ( yes "d" | git mergetool file11 >/dev/null 2>&1 ) &&
#           ( yes "d" | git mergetool file12 >/dev/null 2>&1 ) &&
#           ( yes "l" | git mergetool submod >/dev/null 2>&1 ) &&
#           test "$(cat file1)" = "master updated" &&
#           test "$(cat file2)" = "master new" &&
#           test "$(cat subdir/file3)" = "master new sub" &&
#           test "$(cat submod/bar)" = "branch1 submodule" &&
#           git commit -m "branch1 resolved with mergetool"
#

--- 8< ------ 8< ------ 8< ------ 8< ------ 8< ------ 8< ---

Due to ">dev/null 2>&1", all of the error clues are hidden, and I
didn't dig further to see which one was failing (this is why tests
shouldn't do these in general).