The previous use of require caused File.join on several occasions to
calculate different paths to the same library, depending on which
__FILE__ the library was being calculated as relative to; e.g.
/some/path/prefix/spec/one/bar.rb would do the equivalent of:
require '/some/path/prefix/spec/one/../../libraries/foo/mylib.rb'
and /some/path/prefix/spec/two/baz.rb would do the equivalent of:
require '/some/path/prefix/spec/two/../../libraries/foo/mylib.rb'
This would result in mylib.rb being loaded multiple times, causing
warnings from constants being redefined, and worse, multiple objects
representing the same class hierarchy (@@foo) variables. The latter
actually broke the @@subclasses registration mechanism in
Pacemaker::CIBObject.
By switching to File.expand_path, we ensure we always refer to each
library using a single absolute path, which means Ruby's require
mechanism works as it should, only loading the code the first time
round.
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