Replace the iter/itertext methods of Element in _elementtree with true C implementations, instead of the bootstrapped Python code. In addition to being cleaner (removing the last remains of the bootstrapping code in _elementtree), this gives a 10x performance boost for iter() on large documents.
Also reorganized the tests a bit to be more robust.

Patch by Robin Schreiber.

Patch by Robin Schreiber.

in struct tm, time.struct_time objects returned by time.gmtime(),
time.localtime() and time.strptime() functions now have tm_zone and
tm_gmtoff attributes.  Original patch by Paul Boddie.

Fix also its value on Windows and Linux according to its documentation:
"adjustable" indicates if the clock *can be* adjusted, not if it is or was
adjusted.

In most cases, it is not possible to indicate if a clock is or was adjusted.

2) Abort the loop for all specials, not only infinity.

3) Make the function more general and distinguish between zero clamping
   and folding down the exponent. The latter case is currently handled
   by setting context->clamp to 0 before calling the function.

method

Patch by Hallvard B Furuseth.

  Berch)

2) Remove micro optimization (inline checking for NaN before calling
   mpd_qcheck_nans()) that probably has no benefit in this case.

2) Switch argument order to match the function signature of mpd_calloc()
   (cosmetic change, since the order is irrelevant).

The behavior of MessageDefect is legacy behavior.  The chances anyone is
actually using the undocumented 'line' attribute is low, but it costs
little to retain backward compatibility.  Although one of the costs is
having to restore normal exception behavior in HeaderDefect.  On the
other hand, I'll probably add some specialized behavior there later.