Speed up compilation of specs when there are .suites in the project.

Previously any change to any specification (.spec/.feature/.suite) would trigger compilation of all .suite files, which became combinatorial.
This change:
- restricts triggering changes to the type identity of the top level Specification in a spec file (i.e. all other changes are very quick)
- triggers suite compile only if the changed specs are referenced by the suite (as resolved by the regular expressions (PatternReferences) in the .suite file)
- probably fixes compilation of suites when a spec file is deleted
Merge pull request #153 from timw/feature/faster-spec-build

Speed up compilation of specs when there are .suites in the project