[PATCH v4 00/31] libxl child process handling

[Ian Jackson <ian.jackson@eu.citrix.com>]

This series has now been tested and is in a suitable form for review
and, if thought fit, committing to xen-unstable.  It still culminates
in a patch to convert bootloader execution to the new event machinery.

Changes since v3 ("[RFC PATCH 00/20]") include:
 - All comments on previous version addressed.
 - Several new bugfix patches etc., marked with * below.
 - Broke the bootloader execution rewrite up into three patches.
 - Testing and consequent fixes (only to previously un-acked patches);
   in particular, the final patch has some significant changes.

Bugfixes for problems reported by Roger Pau Monne:
  02/31 libxl: ao: allow immediate completion
  03/31 libxl: fix hang due to libxl__initiate_device_remove
  04/31 libxl: Fix eventloop_iteration over-locking
* 05/31 libxl: remove poller from list in libxl__poller_get

Other general bugfixes:
* 01/31 .gitignore: Add a missing file
  06/31 libxl: Fix leak of ctx->lock
  07/31 tools: Correct PTHREAD options in config/StdGNU.mk
  08/31 libxl: Use PTHREAD_CFLAGS, LDFLAGS, LIBS
  09/31 tools: Use PTHREAD_CFLAGS, _LDFLAGS, _LIBS
  26/31 libxl: Clean up setdefault in do_domain_create
  30/31 libxl: make libxl_create_logfile const-correct

Clarifications and improvements related to memory allocation:
  10/31 libxl: Crash (more sensibly) on malloc failure
  11/31 libxl: Make libxl__zalloc et al tolerate a NULL gc

Preparatory work:
  12/31 libxl: Introduce some convenience macros
  13/31 libxl: include <ctype.h> and introduce CTYPE helper macro
  14/31 libxl: Provide libxl_string_list_length
  15/31 libxl: include <_libxl_paths.h> in libxl_internal.h
  16/31 libxl: abolish libxl_ctx_postfork
* 23/31 autoconf: New test for openpty et al.
* 24/31 libxl: provide libxl__remove_file et al.
* 25/31 libxl: Introduce libxl__sendmsg_fds and libxl__recvmsg_fds

Event-related infrastructure and fixes:
  17/31 libxl: libxl_event.c:beforepoll_internal, REQUIRE_FDS
  18/31 libxl: Protect fds with CLOEXEC even with forking threads
* 19/31 libxl: provide STATE_AO_GC
* 20/31 libxl: handle POLLERR, POLLHUP, POLLNVAL properly
* 21/31 libxl: support multiple libxl__ev_fds for the same fd
  22/31 libxl: event API: new facilities for waiting for subprocesses
  27/31 libxl: provide libxl__datacopier_*
  28/31 libxl: provide libxl__openpty_*
  29/31 libxl: ao: Convert libxl_run_bootloader
* 31/31 libxl: log bootloader output