config: accept “smart” as popup_during_fullscreen parameter (Thanks supplantr)

This was the default, so explicitly setting it is not really necessary,
but of course it should be possible.

fixes #967

parser-specs/config.spec

@@ -229,7 +229,7 @@ state RESTART_STATE:
 
 # popup_during_fullscreen
 state POPUP_DURING_FULLSCREEN:
-  value = 'ignore', 'leave_fullscreen'
+  value = 'ignore', 'leave_fullscreen', 'smart'
       -> call cfg_popup_during_fullscreen($value)
 
 # client.background <hexcolor>

src/config_directives.c

@@ -392,8 +392,13 @@ CFGFUN(restart_state, const char *path) {
 }
 
 CFGFUN(popup_during_fullscreen, const char *value) {
-    config.popup_during_fullscreen =
-        (strcmp(value, "ignore") == 0 ? PDF_IGNORE : PDF_LEAVE_FULLSCREEN);
+    if (strcmp(value, "ignore") == 0) {
+        config.popup_during_fullscreen = PDF_IGNORE;
+    } else if (strcmp(value, "leave_fullscreen") == 0) {
+        config.popup_during_fullscreen = PDF_LEAVE_FULLSCREEN;
+    } else {
+        config.popup_during_fullscreen = PDF_SMART;
+    }
 }
 
 CFGFUN(color_single, const char *colorclass, const char *color) {

testcases/t/201-config-parser.t

@@ -144,6 +144,27 @@ is(parser_calls($config),
    $expected,
    'floating_minimum_size ok');
 
+################################################################################
+# popup_during_fullscreen
+################################################################################
+
+$config = <<'EOT';
+popup_during_fullscreen ignore
+popup_during_fullscreen leave_fullscreen
+popup_during_fullscreen SMArt
+EOT
+
+$expected = <<'EOT';
+cfg_popup_during_fullscreen(ignore)
+cfg_popup_during_fullscreen(leave_fullscreen)
+cfg_popup_during_fullscreen(smart)
+EOT
+
+is(parser_calls($config),
+   $expected,
+   'popup_during_fullscreen ok');
+
+
 ################################################################################
 # floating_modifier
 ################################################################################