Allow config file to specify Signed-off-by identity in format-patch.

Allow config file to specify Signed-off-by identity in format-patch.

Unlike git-commit, git-format-patch was not picking up and using the
user.email config variable for the email part of the committer info.
I was forced to use the GIT_COMMITTER_EMAIL environment variable to
override the default <redacted>. The fix was to
simply move the call to setup_ident() to come before the git_config()
call.

Signed-off-by: Ramsay Allan Jones <redacted>
Acked-by: Johannes Schindelin <redacted>
Signed-off-by: Junio C Hamano <redacted>