Allow putDirectory to continue even if an individual file transfer fails

The current WebDAV wagon implements putDirectory as a recursive sequence of individual put commands for the individual files. This means that failure of an individual put will abort the entire putDirectory.

This, of course, is generally correct and desired behaviour. However, in a few cases it may not be critical that all files in a directory are correctly uploaded. The use case in mind here is uploading Maven sites to not 100% reliable DAV resources, e.g. Google Code (see also WAGON-319).

The request would be thus to add a "continueOnFailure" option (or similar) which would not throw a TransferFailureException if put fails, but instead log a warning or similar. This option would be false by default.

Admittedly, the better/"correct" place to address this issue would be in the code that calls the wagon (in the case of this example, in the Maven Site plugin), because it can make the context-specific decision of whether to be lenient with errors or not.
However, there is no "putDirectoryLeniently" wagon method that the parent can call, and this use case does not seem significant enough to merit changing the wagon interface.