fix record "run" regression

This fixes the record "run" regression pointed out by Marc Khouzam:

    https://sourceware.org/ml/gdb/2014-06/msg00096.html

The bug is that target_require_runnable must agree with the handling
of the "run" target, but currently it is out of sync.  This patch
fixes the problem by changing target_require_runnable to also ignore
the record_stratum.

Built and regtested on x86-64 Fedora 20.
New test case included.

2014-07-14  Tom Tromey  <tromey@redhat.com>

	* target.c (target_require_runnable): Also check record_stratum.
	Update comment.

2014-07-14  Tom Tromey  <tromey@redhat.com>

	* gdb.reverse/rerun-prec.c: New file.
	* gdb.reverse/rerun-prec.exp: New file.