Restore v21 behavior of --directories

Prior to 68b4ce5, the -d flag ensured that search results included
directories. After that commit, the -d flag acted as a toggle,
*restricting* the results to directories. This change restores the
former behavior and improves the manpage to make this explicit.

Fixes #67.

man/pkgfile.pod

@@ -49,7 +49,7 @@ Return only files which are contained within a bin or sbin directory.
 
 =item B<-d>, B<--directories>
 
-Match directories in search results.
+Additionally include directories in search results.
 
 =item B<-g>, B<--glob>
 

src/pkgfile.cc

@@ -268,14 +268,11 @@ std::unique_ptr<filter::Filter> Pkgfile::BuildFilterFromOptions(
                                              std::move(filter));
     }
 
-    std::unique_ptr<filter::Filter> dir_filter =
-        std::make_unique<filter::Directory>();
     if (!options.directories) {
-      dir_filter = std::make_unique<filter::Not>(std::move(dir_filter));
+      filter = std::make_unique<filter::And>(
+          std::make_unique<filter::Not>(std::make_unique<filter::Directory>()),
+          std::move(filter));
     }
-
-    filter =
-        std::make_unique<filter::And>(std::move(dir_filter), std::move(filter));
   }
 
   return filter;

tests/search.py

@@ -75,6 +75,15 @@ def testSearchDirectories(self):
             testing/dhcpcd
         ''').lstrip('\n'))
 
+        r = self.Pkgfile(['-s', '-d', '/usr/bin/dhcpcd'])
+        self.assertEqual(r.returncode, 0)
+
+        self.assertEqual(
+            r.stdout.decode(),
+            textwrap.dedent('''
+            testing/dhcpcd
+        ''').lstrip('\n'))
+
     def testSearchCaseInsensitive(self):
         r = self.Pkgfile(['-s', '-i', 'mKiNiTcPiO'])
         self.assertEqual(r.returncode, 0)