Automatic HTTP installation mirror selection and path

New full automatic installation method using download.opensuse.org mirror (http) and auto configuration of the path using the product number. download.opensuse.org use mirrorbrain, so it won't be overloaded. The product version is taken from the linuxrc.config file, then the path for the distribution repository is adjusted. The install=auto parameter could be used as a kernel parameter to automatically choose this method (usefull for PXE network install with external mirror). The "Automatic HTTP external mirror" selection is available through dialog box.