dpkg-gensymbols: add source version to the diff label.

Source version is also useful to have in the output. Also format the string
according to dpkg-name rules.

debian/changelog

@@ -87,6 +87,8 @@ dpkg (1.15.6) UNRELEASED; urgency=low
     dpkg-gensymbols is now able to detect NEW/MISSING symbols when patterns are
     present in the symbol file (Closes: #541464). Please note, however, that
     there is no way to detect symbol changes in the pattern match sets.
+  * Add source version to the dpkg-gensymbols diff label, reformat it according
+    to the rules of dpkg-name.
 
   [ Jonathan Nieder ]
   * Fix a file handle leak in “dpkg-deb --info”. Thanks to Raphael Geissert

scripts/dpkg-gensymbols.pl

@@ -280,9 +280,9 @@ if ($compare) {
 		    $output);
 	}
 	my ($a, $b) = ($before->filename, $after->filename);
-	my $diff_label = sprintf("%s (%s %s)",
+	my $diff_label = sprintf("%s (%s_%s_%s)",
 	($ref_symfile->{file}) ? $ref_symfile->{file} : "new_symbol_file",
-	$oppackage, $host_arch);
+	$oppackage, $sourceversion, $host_arch);
 	system("diff", "-u", "-L", $diff_label, $a, $b) if -x "/usr/bin/diff";
     }
 }