Properly implement locking for non-existent resources

[doxavore]

DAV4Rack::Controller#lock raises a NotFound response when the resource doesn't exist. This isn't correct behavior, per RFP4918 sections 7.3 Write Locks and Unmapped URLs and 9.10.4 Locking Unmapped URLs: http://www.webdav.org/specs/rfc4918.html Finder on Mac OS X will not allow you to create files and will revert to treating the server as read-only when it doesn't properly implement this spec form of locking.

I believe the best course of action may be to allow the resource.lock(asked) call, as the resource should decide if it should create itself as a blank file (generally correct per the spec) or do something else.

Is there any reason we can't start by removing the raise NotFound unless resource.exist? line, as resource.exist? has no knowledge that this is an attempt at locking?

[chrisroberts]

Existence check removed. Resolved as of 0.2.8