dpkg-buildpackage: Honor new DEB_SIGN_KEYID environment variable

Use the new environment variable if set, as default value to pass to
gnupg.

Closes: #615813, #719418

Suggested-by: Harald Dunkel <harri@afaics.de>

debian/changelog

@@ -63,6 +63,8 @@ dpkg (1.17.2) UNRELEASED; urgency=low
   * Use a simple list to track packages owning a file, instead of using a
     list of arrays of pointers which waste 10 pointers per non-shared file,
     instead of 1. This significantly reduces dpkg memory usage.
+  * Honor new DEB_SIGN_KEYID environment variable in dpkg-buildpackage.
+    Suggested by Harald Dunkel <harri@afaics.de>. Closes: #615813, #719418
 
   [ Updated programs translations ]
   * German (Sven Joachim).

man/dpkg-buildpackage.1

@@ -19,7 +19,7 @@
 .\" You should have received a copy of the GNU General Public License
 .\" along with this program.  If not, see <http://www.gnu.org/licenses/>.
 .
-.TH dpkg\-buildpackage 1 "2013-04-02" "Debian Project" "dpkg utilities"
+.TH dpkg\-buildpackage 1 "2013-08-31" "Debian Project" "dpkg utilities"
 .SH NAME
 dpkg\-buildpackage \- build binary or source packages from sources
 .
@@ -243,6 +243,12 @@ Show the usage message and exit.
 Show the version and exit.
 .
 .SH ENVIRONMENT
+.TP
+.B DEB_SIGN_KEYID
+If set, it will be used to sign the \fB.changes\fP and \fB.dsc\fP files.
+Overridden by the \fB\-k\fP option.
+
+.SS Reliance on exported environment flags
 Even if \fBdpkg\-buildpackage\fP exports some variables, \fBdebian/rules\fP
 should not rely on their presence and should instead use the
 respective interface to retrieve the needed values.

scripts/dpkg-buildpackage.pl

@@ -111,10 +111,11 @@ sub usage {
 my @debian_rules = ('debian/rules');
 my @rootcommand = ();
 my $signcommand;
-my ($admindir, $signkey, $usepause, $noclean,
+my ($admindir, $usepause, $noclean,
     $cleansource, $since, $maint,
     $changedby, $desc, $parallel);
 my $checkbuilddep = 1;
+my $signkey = defined $ENV{DEB_SIGN_KEYID} ? $ENV{DEB_SIGN_KEYID} : undef;
 my $signforce = 0;
 my $signreleased = 1;
 my $signsource = 1;