t5551: fix expected error output

We should probably get rid of the check of message instead, but in
the meantime this should do.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'sp/smart-http-content-type-check' into pu

* sp/smart-http-content-type-check:
  t5551: fix expected error output
fix clang -Wtautological-compare with unsigned enum

Create a GREP_HEADER_FIELD_MIN so we can check that the field value is
sane and silent the clang warning.

Clang warning happens because the enum is unsigned (this is
implementation-defined, and there is no negative fields) and the check
is then tautological.

Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
Signed-off-by: John Keeping <john@keeping.me.uk>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Merge branch 'jk/suppress-clang-warning' into pu

* jk/suppress-clang-warning:
  fix clang -Wtautological-compare with unsigned enum