mount helper in C committed

[David Zeuthen]

Hey,

I just committed tools/hal-storage-mount.c and changed our fdi files to
use this instead. Major changes from the shell version

 1. Should be a lot easier to audit and a lot more secure as it doesn't
    pull in all of bash

 2. Allow anything without '/' as valid mount point

 3. Throws org.freedesktop.Hal.Device.Volume.MountPointNotAvailable
    if you specifically requested a mount point instead of just
    appending -1.. the frontends (like gnome-mount) is now expected
    to handle this by just appending -1, -2 and so forth themselves.
    Notably this changes the ABI a little bit.

 4. Looks up correct policy, e.g. storage-fixed-mount-change-uid
    if the mount options include uid= and just storage-fixed-mount
    otherwise. Ditto for s/fixed/removable/

 5. Allowed udi= for a number of file systems as our default policy
    doesn't allow this (see policy/txt/*.policy for details)

There's a couple of TODO's left in the code but nothing major. I'd
appreciate if someone would audit it with security in mind.

  $ wc -l hal-system-storage-mount hal-storage-mount.c
  233 hal-system-storage-mount
  718 hal-storage-mount.c

Thanks,
David