Issue #11826: Implement new loading functions for CSS and JS

Two new functions have been added so that MantisBT pages can inform the
MantisBT core (html_api.php in particular) which JavaScript files and
stylesheets to load during the output HTML rendering.

These functions must be used PRIOR to html_top() being executed as after
that point of time it'll be too late to load new scripts or stylesheets.

This functionality will prevent multiple inclusions of the same
JavaScript file and will also prevent the need for downloading a new
stylesheet or script half way through the rendering of the page within
the user's browser.

core/html_api.php

@@ -112,6 +112,9 @@
 # flag for error handler to skip header menus
 $g_error_send_page_header = true;
 
+$g_stylesheets_included = array();
+$g_scripts_included = array();
+
 /**
  * Sets the url for the rss link associated with the current page.
  * null: means no feed (default).
@@ -343,18 +346,26 @@ function html_title( $p_page_title = null ) {
 	echo '</title>', "\n";
 }
 
+function require_css( $p_stylesheet_path ) {
+	global $g_stylesheets_included;
+	$g_stylesheets_included[$p_stylesheet_path] = $p_stylesheet_path;
+}
+
 /**
  * (5) Print the link to include the css file
  * @return null
  */
 function html_css() {
+	global $g_stylesheets_included;
 	html_css_link( config_get( 'css_include_file' ) );
 	html_css_link( 'jquery-ui.css' );
-
 	# Add right-to-left css if needed
-	if( lang_get( 'directionality' ) == 'rtl' ) {
+	if ( lang_get( 'directionality' ) == 'rtl' ) {
 		html_css_link( config_get( 'css_rtl_include_file' ) );
 	}
+	foreach ( $g_stylesheets_included as $t_stylesheet_path ) {
+		html_css_link ( $t_stylesheet_path );
+	}
 }
 
 /**
@@ -401,17 +412,27 @@ function html_meta_redirect( $p_url, $p_time = null, $p_sanitize = true ) {
 	return true;
 }
 
+function require_js( $p_script_path ) {
+	global $g_scripts_included;
+	$g_scripts_included[$p_script_path] = $p_script_path;
+}
+
 /**
  * (6a) Javascript...
  * @return null
  */
 function html_head_javascript() {
-	if( ON == config_get( 'use_javascript' ) ) {
+	if ( config_get( 'use_javascript' ) ) {
+		global $g_scripts_included;
+		echo '<script type="text/javascript" src="' . helper_mantis_url( 'javascript_config.php' ) . '"></script>' . "\n";
 		echo '<script type="text/javascript" src="' . helper_mantis_url( 'javascript_translations.php' ) . '"></script>' . "\n";
 		html_javascript_link( 'ajax.js' );
 		html_javascript_link( 'jquery.js' );
 		html_javascript_link( 'jquery-ui.js' );
 		html_javascript_link( 'common.js' );
+		foreach ( $g_scripts_included as $t_script_path ) {
+			html_javascript_link( $t_script_path );
+		}
 	}
 }