linode module presumes curl support is available

Whilst testing this neat new module (6.x-1.x-federico branch)! I was getting the following error when attempting to save my linode key:

Fatal error: Call to undefined function curl_init() in ######/sites/all/modules/linode/linode.admin.inc on line 193

Anyway, I've written a little patch (attached) into the .install file to check for curl, and warn the user on their status report page if it isn't available (could easily be tweaked to detect and report of curl failure during the install too).

FYI: For any users experiencing this error, if you have root access on your linode instance, and are running debian or ubuntu, a simple 'apt-get install php5-curl' and then 'service apache2 restart' will fix the problem.