Improve the .rvmrc by;  * allowing it to auto-install the appropriate ruby it it fails to find one  * Guessing the gemset name based on the JOB_NAME environment variables (useful in buildr) but defaulting to the dir name  * Cleaning up the gems to remove older versions
Improve the .rvmrc by;
 * allowing it to auto-install the appropriate ruby it it fails to find one
 * Guessing the gemset name based on the JOB_NAME environment variables (useful in buildr) but defaulting to the dir name
 * Cleaning up the gems to remove older versions


git-svn-id: d8f3215415546ce936cf3b822120ca56e5ebeaa0@1388938 13f79535-47bb-0310-9956-ffa450edef68

apache/buildr,mariusk/buildr-kawa,jpcaruana/buildr,stewi2/buildr,liamchristopher/buildr,stewi2/buildr,mariusk/buildr-kawa,stewi2/buildr,jpcaruana/buildr,liamchristopher/buildr,mariusk/buildr-kawa,liamchristopher/buildr,jpcaruana/buildr,liamchristopher/buildr,apache/buildr,apache/buildr,stewi2/buildr,jpcaruana/buildr,apache/buildr