let .rvmrc complain about not existing ruby instead of breaking systems

.rvmrc

@@ -1,13 +1,23 @@
 #!/bin/bash
+
+rubygems_version="1.8.24"
+ruby_version="1.9.3-p194"
+gemset="diaspora"
+
 if [ -e '.rvmrc.local' ]; then
   source .rvmrc.local;
 elif [ -e '.rvmrc_custom' ] ; then
   source .rvmrc_custom;
 else
-  rvm --create use ruby-1.9.3-p194@diaspora
+  if rvm list strings | grep -q "$ruby_version" ; then
+    rvm --create use "$ruby_version@$gemset"
+  else
+    echo -e "\e[00;31mPLEASE INSTALL RUBY $ruby_version WITH \`rvm install $ruby_version\`"
+    echo -e "Don't forget to run \`cd .. && cd -\` afterwards!\e[00m"
+    return 1
+  fi
 fi
 
-rubygems_version="1.8.24"
 
 if [ "$(gem --version)" != "$rubygems_version" ]; then
   rvm rubygems "$rubygems_version"