Avoid absolute url for local resources

A problem arises if accessing the site through HTTPS when SITEURL is defined as HTTP instead of HTTPS (which make sense). 
The resource will fail to load if accessed as HTTPS with the following message: "The page at 'https://blablabla' was loaded over HTTPS, but ran insecure content from 'http://blablabla/theme/css/style.css': this content should also be loaded over HTTPS."