add L4_TimePoint(), other support to <l4/types.h>
testbench: add the "type" suite

Anothe day, another test suite. This one is about the basic types exported in
<l4/types.h>. Things such as the behaviour of L4_Fpage(), L4_FpageLog2(), and
L4_TimePeriod() may appear in the future; for now it's just for TimePoints.
testbench: type: add validity checking test for TimePoint values

This looks good enough to put into <l4/types.h> as yet another _NP() function,
eventually, after the tests have been refined to vary the time base also. I
don't suppose it makes any difference (given the "replace these bits and maybe
bump" semantics), but an arbitrary parameter should have a bunch of other
values, too.
accept TimePoint values in wakeup_at()

Expired TimePoints are handled as L4_ZeroTime.

Also a test for using TimePoints in L4_Sleep(). Seems to work just fine
regardless of pre-delay, but could be more comprehensive.
testbench: use thread.c TSD in idlsupp.c

Don't know why it was something else, earlier.
testbench: add macros for declaring IDL dispatch fixtures
ipc: support TimePoint values in the XferTimeouts TCR

The way this changeset works depends entirely on pt_is_valid() returning
correct values for as long as it may appear in eval_xfer_timeout(). Neither
for how long it'll keep returning false during invalidity, nor how long a
latency there may be between expiration and observation, is known as of this
changeset.

Really, all timeouts should be evaluated at sys_ipc() as that's when their
translations are most likely to not have expired too long ago.
testbench: ipc: test TimePoint values in XferTimeouts

Changes besides the test proper:
  - add quit_cond parameter to IDL_FIXTURE()
  - ... and use that to make helper_quit_impl() re-entrant
  - export flush_byte_range() from string_suite.c
  - copy the mock L4.X2 IDL source from µIDL (and FaultHandler's sole label)