Updated Diff Web API command.

Made it so it won't crash if the change list is very large.
Now supports classic "diff" as well as just geometry changes.
Added all option to featureDiff so that i can get all attributes for a feature through the web-api.

Also fixed Diff to return the feature path instead of the id.
Merge pull request #253 from volaya/null_id

Added support for parsing partial representations of the null id
Minor changes to pull request.

Fixed compilation error in man page.
Fixed typo in history manual page.
Removed unneeded warning suppression.
Fixed test failure in LogOpPerformanceTest.
Merge branch 'log_improvements'
Merge pull request #243 from jdgarrett/webdiff

Updated Diff Web API command.
Added additional plumbing commands (ls-tree, cat, rev-list, merge-base, diff-tree and show-ref).

Changed help command to show just porcelain commands.

Porcelain command for listing a path is now called "ls".

Added documentation for plumbing commands and removed it from manual