dpkg-maintscript-helper: Document environment requirements for supports

Closes: #739634

debian/changelog

@@ -7,6 +7,8 @@ dpkg (1.17.8) UNRELEASED; urgency=low
     - Improve Perl code coverage.
     - Improve C code coverage.
   * Handle space-only strings when parsing versions in libdpkg.
+  * Document the environment requirements for the dpkg-maintscript-helper
+    supports command in the man page. Closes: #739634
 
   [ Updated programs translations ]
   * German (Sven Joachim).

man/dpkg-maintscript-helper.1

@@ -15,7 +15,7 @@
 .\" You should have received a copy of the GNU General Public License
 .\" along with this program.  If not, see <https://www.gnu.org/licenses/>.
 .
-.TH dpkg\-maintscript\-helper 1 "2014-04-01" "Debian Project" "dpkg suite"
+.TH dpkg\-maintscript\-helper 1 "2014-04-28" "Debian Project" "dpkg suite"
 .SH NAME
 dpkg\-maintscript\-helper \- works around known dpkg limitations in maintainer scripts
 .
@@ -25,6 +25,8 @@ dpkg\-maintscript\-helper \- works around known dpkg limitations in maintainer s
 .
 .SH COMMANDS AND PARAMETERS
 .P
+\fBsupports\fP \fIcommand\fP
+.P
 \fBrm_conffile\fP \fIconffile\fP [\fIprior-version\fP [\fIpackage\fP]]
 .P
 \fBmv_conffile\fP \fIold-conffile\fP \fInew-conffile\fP [\fIprior-version\fP [\fIpackage\fP]]
@@ -233,3 +235,8 @@ the currently installed \fBdpkg\fP:
     if dpkg\-maintscript\-helper supports \fIcommand\fP; then
         dpkg\-maintscript\-helper \fIcommand\fP ...
     fi
+.P
+The command \fBsupports\fP will return 0 on success, 1 otherwise. The
+\fBsupports\fP command will check if the required environment variables
+by the script as set by dpkg have been setup, and will consider it a
+failure in case the environment is not sufficient.