t/lib-credential: use write_script

Use write_script to create the helper "askpass" script, instead of
hand-creating it with hardcoded "#!/bin/sh" to make sure we use the
shell the user told us to use.

Signed-off-by: Ben Walton <bdwalton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'hj/pretty-naked-decoration'

The pretty-format specifier "%d", which expanded to " (tagname)"
for a tagged commit, gained a cousin "%D" that just gives the
"tagname" without frills.

* hj/pretty-naked-decoration:
  pretty: add %D format specifier
Merge branch 'da/rev-parse-verify-quiet'

"rev-parse --verify --quiet $name" is meant to quietly exit with a
non-zero status when $name is not a valid object name, but still
gave error messages in some cases.

* da/rev-parse-verify-quiet:
  stash: prefer --quiet over shell redirection of the standard error stream
  refs: make rev-parse --quiet actually quiet
  t1503: use test_must_be_empty
  Documentation: a note about stdout for git rev-parse --verify --quiet
Merge branch 'rs/graph-simplify'

* rs/graph-simplify:
  graph: simplify graph_padding_line()
Merge branch 'rs/remote-simplify'

* rs/remote-simplify:
  remote: simplify match_name_with_pattern() using strbuf
Merge branch 'sb/t9300-typofix'

* sb/t9300-typofix:
  t9300-fast-import: fix typo in test description
Merge branch 'sb/t6031-typofix'

* sb/t6031-typofix:
  t6031-test-merge-recursive: do not forget to add file to be committed
Merge branch 'jk/mbox-from-line'

Some MUAs mangled a line in a message that begins with "From " to
">From " when writing to a mailbox file and feeding such an input
to "git am" used to lose such a line.

* jk/mbox-from-line:
  mailinfo: work around -Wstring-plus-int warning
  mailinfo: make ">From" in-body header check more robust
Update draft release notes to 2.2
Merge branch 'bw/use-write-script-in-tests' into next

* bw/use-write-script-in-tests:
  t/lib-credential: use write_script
Merge branch 'master' into next

* master:
  Update draft release notes to 2.2