Add big fat warning if attempting to run Gitorious on wrong Ruby version
user
```ruby
if !%w[1.8.7 1.9.3].include?(RUBY_VERSION)
  $stderr.puts <<-WARN
######################################################################
#                              WARNING!                              #
######################################################################
#                                                                    #
# Your Ruby version, #{RUBY_VERSION} may not be supported. Gitorious #
# has only been tested with Ruby 1.8.7 and 1.9.3. Please consider    #
# using one of these officially supported versions. If you feel that #
# this warning has been issued in error, please let us know at       #
# http://groups.google.com/group/gitorious/                          #
#                                                                    #
# Please note that Ruby 1.9.1 and 1.9.2 should not be used. Upgrade  #
# to 1.9.3.                                                          #
#                                                                    #
######################################################################
  WARN
end
```
assistant