Avoid having 'remote: /some/path' in the gemfile.locks

When using bundler's "gemspec" setting it hardcodes a
local path as the "remote". This causes every 'bundle install' or
similar invocation on any other workstation to change that file simply
because the remote has changed. Not good.

Work around it by evaluating the gemspec ourselves and generating the
gem dependency list from that.

Same effect, better result, I think.