Teach procstat_get_shm_info_kvm() how to fetch the pathname of a SHM file
descriptor from a core and set it in fts->fs_path.

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 the fo_stat() method of shared memory objects and shm_path() to
  export the path, mode, and size of a shared memory object via
  struct kinfo_file.
- Add a struct shmstat to the libprocstat(3) interface along with a
  procstat_get_shm_info() to export the mode and size of a shared memory
  object.
- 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.

General mdoc(7) and typo fixes.

PR:		167734

capability mode and capabilities.

Right now no attempt is made to unwrap capabilities when operating on
a crashdump, so further refinement is required.

Approved by:	re (bz)
Sponsored by:	Google Inc

Requested by:	stas

Reviewed by:	jilles, gjb

Now libprocstat takes care of its own dependencies and does not
require applications to specify them.

Reviewed by:	stas, jilles

If a file is mapped with with MAP_PRIVATE, no write permission is required
and changes do not end up in the file. Therefore, tools like fuser and fstat
should not show the file as open for writing.

The protection as displayed by procstat -v still includes write in this
case, and shows 'C' for copy-on-write.