Add Pre-Depends on tar >= 1.23 to dpkg

That's the tar version introducing the ‘--warning=no-timestamp’ option,
which dpkg started to use due to #640298. The version is satisfied in
stable, but making the dependency explicit is useful for systems
upgrading from oldstable directly to testing (or next stable), even if
that's not generally supported.

Closes: #642802

debian/changelog

@@ -22,6 +22,8 @@ dpkg (1.16.2) UNRELEASED; urgency=low
   * Improve error message in dpkg-gencontrol and dpkg-gensymbols when
     debian/control does not have any package stanza. Closes: #642473
     Based on a patch by Kyle Willmon <kylewillmon@gmail.com>.
+  * Add Pre-Depends on tar >= 1.23 (satisfied in stable) to dpkg due to it
+    using the ‘--warning=no-timestamp’ option. Closes: 642802
 
   [ Raphaël Hertzog ]
   * Update Dpkg::Shlibs to look into multiarch paths when cross-building

debian/control

@@ -31,7 +31,7 @@ Description: Debian package management static library
 Package: dpkg
 Architecture: any
 Essential: yes
-Pre-Depends: ${shlibs:Depends}, xz-utils
+Pre-Depends: ${shlibs:Depends}, tar (>= 1.23), xz-utils
 Depends: ${misc:Depends}
 Breaks: dpkg-dev (<< 1.15.8), libdpkg-perl (<< 1.15.8),
  apt (<< 0.7.7), aptitude (<< 0.4.7-1),