MFC 233760:

MFC 233760:
Export some more useful info about shared memory objects to userland
via procstat(1) and fstat(1):
- Change shm file descriptors to track the pathname they are associated
  with and add a shm_path() method to copy the path out to a caller-supplied
  buffer.
- Use shm_path() to export the path of a shared memory object via
  struct kinfo_file.
- Change procstat to always print out the path for a given object if it
  is valid.
- Teach fstat about shared memory objects and to display their path,
  mode, and size.

git-svn-id: svn://svn.freebsd.org/base/stable/8@236699 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f