Add file missed from last commit.
Rename test.

I realized that the name of this test only made sense when considering
the old (never committed) implementation of the fix that came along
with the test originally, that forced a schedlock while a step-resume
(to get over the signal handler) was inserted.  The final solution
that went into the tree does not force that locking.

So this renames it to something more descriptive.

gdb/testsuite/
2014-02-21  Pedro Alves  <palves@redhat.com>

	* gdb.threads/step-after-sr-lock.c: Rename to ...
	* gdb.threads/signal-while-stepping-over-bp-other-thread.c: ... this.
	* gdb.threads/step-after-sr-lock.exp: Rename to ...
	* gdb.threads/signal-while-stepping-over-bp-other-thread.exp:
	... this.
Fix length arg in call to breakpoint_xfer_memory.

The patch "return target_xfer_status in to_xfer_partial" caused a
regression in various s390(x) test cases, because memory_xfer_partial
filled only the first byte of the read buffer from a breakpoint shadow:

    https://sourceware.org/ml/gdb-patches/2014-01/msg01071.html

This patch fixes the regression.