Fix for checkout —theirs or checkout —ours not working if theirs or ours was a deleted node.
Added time support for the web api log command.

There was an assumption that since and until were ObjectIds, so I added
new parameters for a date range.
The feature diff web op now operates on any treeish.

It previously only worked with Commit IDs.
The commit web api response now includes the commit ID.
Added a method of summarizing a log command.

If summarize is specified, it will return the first and last commit and the number of commits
in the log.
Added Export CSV command to web api.