Define constants for Plugin Priority

Previously, these values were hardcoded.

Note that the priority for the MantisCore pseudo-plugin is now set to
HIGHEST instead of 3 previously. This avoids creating another constant,
considering that it makes sense to load this first anyway.

As suggested by @atrol in [[1]].

[1]: #1700 (comment)

core/constant_inc.php

@@ -233,6 +233,10 @@
 define( 'CONFIRMATION_TYPE_WARNING', 1 );
 define( 'CONFIRMATION_TYPE_FAILURE', 2 );
 
+# Plugin management
+define( 'PLUGIN_PRIORITY_LOW', 1 );
+define( 'PLUGIN_PRIORITY_HIGH', 5 );
+
 # error messages
 define( 'ERROR_PHP', -1 );
 define( 'ERROR_GENERIC', 0 );

core/plugin_api.php

@@ -95,8 +95,8 @@ function plugin_pop_current() {
 function plugin_get_force_installed() {
 	$t_forced_plugins = config_get_global( 'plugins_force_installed' );
 
-	# MantisCore pseudo-plugin is force-installed by definition, with priority 3
-	$t_forced_plugins['MantisCore'] = 3;
+	# MantisCore pseudo-plugin is force-installed by definition
+	$t_forced_plugins['MantisCore'] = PLUGIN_PRIORITY_HIGH;
 
 	return $t_forced_plugins;
 }

core/print_api.php

@@ -1262,12 +1262,14 @@ function print_custom_field_projects_list( $p_field_id ) {
  * @return void
  */
 function print_plugin_priority_list( $p_priority ) {
-	if( $p_priority < 1 || $p_priority > 5 ) {
+	if( $p_priority < PLUGIN_PRIORITY_LOW || $p_priority > PLUGIN_PRIORITY_HIGH ) {
 		echo '<option value="', $p_priority, '" selected="selected">', $p_priority, '</option>';
 	}
 
-	for( $i = 5;$i >= 1;$i-- ) {
-		echo '<option value="', $i, '" ', check_selected( $p_priority, $i ), ' >', $i, '</option>';
+	for( $i = PLUGIN_PRIORITY_HIGH; $i >= PLUGIN_PRIORITY_LOW; $i-- ) {
+		echo '<option value="', $i, '"';
+		check_selected( $p_priority, $i );
+		echo '>', $i, '</option>';
 	}
 }
 

manage_plugin_update.php

@@ -64,7 +64,7 @@
 	}
 
 	$f_priority = gpc_get_int( 'priority_'.$t_basename, 3 );
-	if( $f_priority < 1 || $f_priority > 5 ) {
+	if( $f_priority < PLUGIN_PRIORITY_LOW || $f_priority > PLUGIN_PRIORITY_HIGH ) {
 		error_parameters( 'priority_' . $t_basename );
 		trigger_error( ERROR_INVALID_FIELD_VALUE, ERROR );
 	}