dpkg-query: Document that --list and --show arguments are optional

Do that in the --help output and in the man page.

debian/changelog

@@ -39,6 +39,8 @@ dpkg (1.16.0) UNRELEASED; urgency=low
   * Sync the info database directory on unpack instead of the temporary
     control information directory, and print the correct pathname on error
     instead of the last file acted on that directory.
+  * Document in dpkg-query --help output and man page that --list and --show
+    arguments are optionsl.
 
   [ Raphaël Hertzog ]
   * Fail properly when debian/source/format is empty. Closes: #600854

man/dpkg-query.1

@@ -12,7 +12,7 @@ the \fBdpkg\fP database.
 .
 .SH COMMANDS
 .TP
-.BR \-l ", " \-\-list " \fIpackage-name-pattern\fP..."
+.BR \-l ", " \-\-list " [\fIpackage-name-pattern\fP...]"
 List packages matching given pattern. If no \fIpackage-name-pattern\fP
 is given, list all packages in \fI/var/lib/dpkg/status\fP, excluding
 the ones marked as not-installed (i.e. those which have been previously
@@ -65,7 +65,7 @@ automatically to fit the terminal width. It is intended for human
 readers, and is not easily machine-readable. See \fB\-W\fP (\fB\-\-show\fP)
 and \fB\-\-showformat\fP for a way to configure the output format.
 .TP
-.BR \-W ", " \-\-show " \fIpackage-name-pattern\fP..."
+.BR \-W ", " \-\-show " [\fIpackage-name-pattern\fP...]"
 Just like the \fB\-\-list\fP option this will list all packages matching
 the given pattern. However the output can be customized using the
 \fB\-\-showformat\fP option.

src/querycmd.c

@@ -612,7 +612,7 @@ usage(const struct cmdinfo *ci, const char *value)
 "  -p|--print-avail <package> ...   Display available version details.\n"
 "  -L|--listfiles <package> ...     List files `owned' by package(s).\n"
 "  -l|--list [<pattern> ...]        List packages concisely.\n"
-"  -W|--show <pattern> ...          Show information on package(s).\n"
+"  -W|--show [<pattern> ...]        Show information on package(s).\n"
 "  -S|--search <pattern> ...        Find package(s) owning file(s).\n"
 "  -c|--control-path <package> [<file>]\n"
 "                                   Print path for package control file.\n"