patchbuiltin/send-pack.c: Respect http.signingkey

> From: Junio C Hamano <gitster@pobox.com>
>
> Prior to this patch, when git-send-pack was exec'ed, as is done by
> git-remote-http, it did not reread the config, so it did not respect
> the configured value of http.signingkey. Thus it was impossible to
> specify a signing key over HTTP, other than the default key in the
> keyring having a User ID matching the "Name <email>" format.
>
> This patch at least partially fixes the problem by reading in the GPG
> config from within send-pack. It does not address the related problem
> of plumbing a value for this configuration option using
> `git -c http.signingkey push ...`.

>
> Signed-off-by: Dave Borowitz <dborowitz@google.com>
> ---
>  builtin/send-pack.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/builtin/send-pack.c b/builtin/send-pack.c
> index b961e5a..23b2962 100644
> --- a/builtin/send-pack.c
> +++ b/builtin/send-pack.c
> @@ -11,6 +11,7 @@
>  #include "transport.h"
>  #include "version.h"
>  #include "sha1-array.h"
> +#include "gpg-interface.h"
>  
>  static const char send_pack_usage[] =
>  "git send-pack [--all | --mirror] [--dry-run] [--force] [--receive-pack=<git-receive-pack>] [--verbose] [--thin] [--atomic] [<host>:]<directory> [<ref>...]\n"
> @@ -113,6 +114,8 @@ int cmd_send_pack(int argc, const char **argv, const char *prefix)
>  	int from_stdin = 0;
>  	struct push_cas_option cas = {0};
>  
> +	git_config(git_gpg_config, NULL);
> +
>  	argv++;
>  	for (i = 1; i < argc; i++, argv++) {
>  		const char *arg = *argv;