debian: Add perl:Depends substvar to dpkg-dev package Depends

The scripts use modules not present in perl-base, so to be entirely
correct we require the perl package, even though it gets pulled anyway
by the libdpkg-perl package.

Warned-by: dpkg-gencontrol

debian/changelog

@@ -138,6 +138,7 @@ dpkg (1.18.11) UNRELEASED; urgency=medium
     - Remove update-alternatives, dpkg-divert and dpkg-statoverride
       compatibility symlinks, again.
     - Use perl:Depends via dh_perl instead of a hardcoded perl in Depends.
+    - Add perl:Depends to dpkg-dev Depends.
     - Remove unused dh_strip from binary_indep target.
     - Remove ancient upgrade code from maintainer scripts (before 1.15.x).
     - Stop compressing the dpkg.deb package with gzip.

debian/control

@@ -83,6 +83,7 @@ Architecture: all
 Multi-Arch: foreign
 Depends:
  ${misc:Depends},
+ ${perl:Depends},
  libdpkg-perl (= ${source:Version}),
 # Needed for --clamp-mtime.
  tar (>= 1.28-1),