Merge kern_descrip.c:1.314, kern_proc.c:1.256, sysctl.h:1.153,

Merge kern_descrip.c:1.314, kern_proc.c:1.256, sysctl.h:1.153,
user.h:1.71 from HEAD to RELENG_7:

  Add two new sysctls in support of the forthcoming procstat(1) to support
  its -f and -v arguments:

  kern.proc.filedesc - dump file descriptor information for a process, if
    debugging is permitted, including socket addresses, open flags, file
    offsets, file paths, etc.

  kern.proc.vmmap - dump virtual memory mapping information for a process,
    if debugging is permitted, including layout and information on
    underlying objects, such as the type of object and path.

  These provide a superset of the information historically available
  through the now-deprecated procfs(4), and are intended to be exported
  in an ABI-robust form.