This patch teaches testutil how to read multi-line input files with
backspace-newline line continuation markers.

The patch also breaks up all the single-line arguments test input files into
multi-line files with lines shorter than 80 characters.

This allows QEMU guests to be started with an arbitrary clock
offset

The test case can't actually be enabled, since QEMU argv expects
an absolute timestring, and this will obviously change every
time the test runs :-( Hopefully QEMU will allow a relative
time offset in the future.

* src/qemu/qemu_conf.c, src/qemu/qemu_conf.h: Use the -rtc arg
  if available to support variable clock offset mode
* tests/qemuhelptest.c: Add QEMUD_CMD_FLAG_RTC for qemu 0.12.1
* qemuxml2argvdata/qemuxml2argv-clock-variable.args,
  qemuxml2argvdata/qemuxml2argv-clock-variable.xml,
  qemuxml2argvtest.c: Test case, except we can't actually enable
  it yet.

We keep support for the pty based monitor so that we can re-connect
to VMs started by older versions of libvirtd.

* src/domain_conf.c: handle formatting and parsing unix monitors

* src/qemu_driver.c: add qemudOpenMonitorUnix(), remove the monitor
  pty path searching from qemudFindCharDevicePTYs(), switch
  qemudStartVMDaemon() and qemuDomainXMLToNative() to using a unix
  monitor

* tests/qemuxml2argvtest.c: switch to using a unix monitor

* tests/qemuxml2argvdata/qemuxml2argv-*.args: update test data

virExec will write out the pid of the daemonized process only. Use this
in the QEMU driver, rather than QEMU's pidfile, so we can catch errors we
might miss if the emulator bails early.

* tests/qemuxml2argvtest.c (testCompareXMLToArgvFiles): Adjust the
code that creates "actual" output, so that it too produces a
newline-terminated buffer.
* tests/qemuxml2argvdata/*.args: Append a newline to each, via:
for i in $(find|grep '\.args$'); do echo >> $i;done