dpkg-deb: Clarify --extract bad usage error message on missing arguments

Make clear that the command requires two arguments, instead of
suggesting only a deb filename is needed, to then requesting a directory
name on a second invocation.

Closes: #718899

debian/changelog

@@ -11,6 +11,8 @@ dpkg (1.17.2) UNRELEASED; urgency=low
   * Automatically prepend needed spaces for continuation --force-help lines.
   * Be more precise on deb format errors with data member in dpkg-deb.
   * Do not allow deb packages with control and data members swapped.
+  * Clarify «dpkg-deb --extract» bad usage error message on missing arguments
+    by printing all required arguments at once. Closes: #718899
 
  -- Guillem Jover <guillem@debian.org>  Sun, 28 Jul 2013 15:06:29 +0200
 

dpkg-deb/extract.c

@@ -414,7 +414,8 @@ do_extract(const char *const *argv)
 
   debar = *argv++;
   if (debar == NULL)
-    badusage(_("--%s needs a .deb filename argument"), cipaction->olong);
+    badusage(_("--%s needs .deb filename and directory arguments"),
+             cipaction->olong);
 
   dir = *argv++;
   if (dir == NULL)
@@ -447,7 +448,8 @@ do_raw_extract(const char *const *argv)
 
   debar = *argv++;
   if (debar == NULL)
-    badusage(_("--%s needs a .deb filename argument"), cipaction->olong);
+    badusage(_("--%s needs .deb filename and directory arguments"),
+             cipaction->olong);
 
   dir = *argv++;
   if (dir == NULL)