[PATCH v2 0/9] enable target-async by default

[Tom Tromey <tromey at redhat dot com>]

Here's version 2 of the series to enable target-async by default.

Version 1 was here:

    http://sourceware.org/ml/gdb-patches/2013-07/msg00716.html

This version addresses the review comments made for the first series.
In particular:

* Adds target_ops pointers to various to_* methods as suggested by
  Markus.  This cleans up the API a bit; and I think is a good
  long-term direction for the target layer.  This is patch 2 now.

* Fixes patch 8 (was patch 7 previously) to account for oddity that
  Doug noticed.

* Adds PR numbers to a couple of ChangeLog entries, suggested by Yao.

Built and regtested on x86-64 Fedora 18.
I also built it on PPC64 Fedora 18 and I did a --host=mingw32 build
using the cross tools in Fedora.

There are still a number of things in patch 2 that have never been
compiled.  However, they seem correct; and anyhow if there is a build
bug, it will be of a trivial nature.