Use wp_content_dir() in mgs_core.

For greater compatibility with future WordPress releases the mgs_core
curl and cdir attributes now use wp_content_dir().

**This requires users on single-site setups to drag their /webcomic
directory from /wp-content into /wp-content/uploads.** Networked setups
should be unaffected (needs further testing).

webcomic-includes/mgs-core.php

@@ -57,9 +57,11 @@ final function __construct() {
 		if ( !$this->file )    $this->file    = __FILE__;
 		if ( !$this->type )    $this->type    = 'plugin';
 
+		$upload = wp_upload_dir();
+
 		$this->base    = ( 'plugin' == $this->type ) ? plugin_basename( $this->file ) : dirname( $this->file );
-		$this->cdir    = ( is_multisite() ) ? BLOGUPLOADDIR : WP_CONTENT_DIR;
-		$this->curl    = ( is_multisite() ) ? trailingslashit( get_bloginfo( 'url' ) ) . 'files' : WP_CONTENT_URL;
+		$this->cdir    = $upload[ 'basdir' ];
+		$this->curl    = $upload[ 'baseurl' ];
 		$this->update  = array();
 		$this->errors  = array();
 		$this->options = $this->option();