Add fuse capabilities support to Mono.Fuse

Hi Jonathan.

I ran into an issue with how fuse handles calls to truncate files on Ubuntu.  In the process of trying to fix this issue, I made a change to Mono.Fuse to enable support for capabilities.

See this l link for some context on the problem:

http://marc.info/?l=fuse-devel&m=129978233712105&w=1

Unfortunately this isn't sufficient to solve the problem for me.  I still had to work around it because the problem appears to be related to the Ubuntu kernel.  Nevertheless, I still think others might find this functionality useful.

Thanks,
Bryan