Adding in ability to remember wantsurl better

- need to set $cfg->externallogin to point to auth/cas/index.php
 rather than the external login site, to save the needed info into
$SESSION

eg $cfg->externallogin = https://[maharasite]/auth/cas/index.php?wantsurl={shorturlencoded}
Merge pull request #7 from robertlyon777/master

Adding in ability to remember wantsurl better