MDL-17549 auth/radius: add CHAP and MSCHAP auth support, detect PHP extension

MDL-17549 auth/radius: add CHAP and MSCHAP auth support, detect PHP extension

     * Added support for CHAP and MSCHAP authentication schemes
       contributed by Stanislav Tsymbalov http://www.tsymbalov.net/
       original code at http://sourceforge.net/projects/moodleradius/
     * Tweak the detection of PHP RADIUS extension and Pear code
     * Update the warning notices to use more Moodly CSS classes

    lib/pear: Add RADIUS and CHAP PEAR libs

     * Add PEAR Auth_RADIUS and Crypt_CHAP packages to lib/pear

Author: Jonathan Harker <jonathan@catalyst.net.nz>