Switch stable/10 back to -PRERELEASE now that releng/10.1 is
branched.

Sponsored by:	The FreeBSD Foundation
MFC r272536:
Add kernel option KSTACK_USAGE_PROF.
MFC r272538:
Slightly reword comment.  Move code, which is described by the
comment, after it.
Merge: r268811

Update to byacc 20140715

PR:             191020
Submitted by:   gcooper (yaneurabeya@gmail.com)
Merge: r272649
 use calloc in get_line() when allocating line to ensure it is fully initialized,
 fixes a later uninitialized value in copy_param() (FreeBSD #193499).

PR: 193499
Submitted by: Thomas E. Dickey  <tom@invisible-island.net>
Merge: 272655

Import byacc 20141005 from vendor
Merge: r272769

Import byacc 20141006

PR: 193499
MFC r272885:
  Do not add late flag when file= is specified because it has a bad
  side-effect.  The specified file should exist before the fstab line.
Merge: r268812

Add the mtree entry for yacc tests