Remote util.unique()
Remove unused objects.readGraphHashes()
Add objects.readAncestors to get all commit ancestors
Add merge.readCommonAncestor
Test readCommonAncestor()
Improve test desc
merge() throws if cannot resolve passed ref
Test merge() throws if cannot resolve passed ref
Throw if try to merge when head detached.

* Git supports this.
Make setup fn available to whole spec
Fix readMostCommonAncestor

* Needed to put add each hash passed to its own list of ancestors to get correct answer for parent -> child (parent)
Enable all tests
merge() throws if passed hash that is not commit
merge() says up to date if fromHash in ancestor of intoHash
Add merge() tests
Todo done
Catch exceptions so node stack trace hidden in CLI use
rm unnessary newline for cli use
Make checkout write index of checked out commit
Fix hashes in tests for correct index values on checkout