rbhdrdir issue with ruby 1.9.1 on ubuntu 10.04 server

[udl]

Hi,

we're having trouble installing ruby_core_source via bundler here.
rbhdrdir is set to /usr/include/ruby-1.9.1 (which is ok)
per default, ubuntu installs ruby-1.9.1 headers in /usr/include/ruby-1.9.1/ruby (NOT ruby-1.9.1-pXX)

it would be nice, if we could pass an option for the hdrdir or something like that.