man: Document the exit codes for dpkg-query

Closes: #571798

debian/changelog

@@ -160,6 +160,7 @@ dpkg (1.15.6) UNRELEASED; urgency=low
     Closes: #430958
   * Document in the man page the effects of setting TMPDIR for dpkg and
     dpkg-deb, HOME for dselect and dpkg and PAGER for dpkg. Closes: #572836
+  * Document the exit codes for dpkg-query. Closes: #571798
 
   [ Modestas Vainius ]
   * Implement symbol patterns (Closes: #563752). From now on, it is possible to

man/dpkg-query.1

@@ -1,4 +1,4 @@
-.TH dpkg\-query 1 "2009-09-06" "Debian Project" "dpkg suite"
+.TH dpkg\-query 1 "2010-03-07" "Debian Project" "dpkg suite"
 .SH NAME
 dpkg\-query \- a tool to query the dpkg database
 .
@@ -152,6 +152,13 @@ run:
   \fBdpkg\-query \-W \-f=\(aq${Package} ${Version}\\t${Maintainer}\\n\(aq dpkg\fP
 .fi
 .
+.SH "EXIT STATUS"
+.IP 0
+The requested query was successfully performed.
+.IP 1
+Problems were encountered while parsing the command line or performing the
+query, including no file or package being found (except for \-\-control\-path).
+.
 .SH ENVIRONMENT
 .TP
 \fBCOLUMNS\fP