test: Accept perl's Lancaster Consensus AUTHOR_TESTING variable

This is the variable perl developers expect when running author or
developer tests, honour it to make people's life easier.

README

@@ -82,9 +82,9 @@ To run the test suite («make check»):
   aspell (optional, author)
   aspell-en (optional, author)
 
-  Define the environment variable DPKG_DEVEL_MODE to run the test suite
-  in development mode, to include tests that might not be pertinent during
-  normal release builds.
+  Define the environment variable DPKG_DEVEL_MODE or AUTHOR_TESTING to run
+  the test suite in development mode, to include tests that might not be
+  pertinent during normal release builds.
 
 To enable additional developer's documentation («make doc») this software
 will be needed:

debian/changelog

@@ -77,6 +77,7 @@ dpkg (1.18.8) UNRELEASED; urgency=medium
       to 99999.
     - Add new pod-spell unit test.
     - Refactor common unit test checks for needed things into Test::Dpkg.
+    - Accept perl's Lancaster Consensus AUTHOR_TESTING variable.
   * Documentation:
     - Improve dpkg-buildpackage(1) on environment expectations.
     - Clarify the format of the db:Status-Abbrev virtual field in

scripts/Test/Dpkg.pm

@@ -54,7 +54,7 @@ sub all_perl_files
 
 sub test_needs_author
 {
-    if (not $ENV{DPKG_DEVEL_MODE}) {
+    if (not $ENV{DPKG_DEVEL_MODE} and not $ENV{AUTHOR_TESTING}) {
         plan skip_all => 'developer test';
     }
 }