an idea from Guido.  This restores that the datetime implementation
never passes a datetime d to a tzinfo method unless d.tzinfo is the
tzinfo instance whose method is being called.  That in turn allows
enormous simplifications in user-written tzinfo classes (see the Python
sandbox US.py and EU.py for fully fleshed-out examples).

d.astimezone(tz) also raises ValueError now if d lands in the one hour
of the year that can't be expressed in tz (this can happen iff tz models
both standard and daylight time).  That it used to return a nonsense
result always ate at me, and it turned out that it seemed impossible to
force a consistent nonsense result under the new implementation (which
doesn't know anything about how tzinfo classes implement their methods --
it can only infer properties indirectly).  Guido doesn't like this --
expect it to change.

New tests of conversion between adjacent DST-aware timezones don't pass
yet, and are commented out.

Running the datetime tests in a loop under a debug build leaks 9
references per test run, but I don't believe the datetime code is the
cause (it didn't leak the last time I changed the C code, and the leak
is the same if I disable all the tests that invoke the only function
that changed here).  I'll pursue that next.

now derive from InterpolationError, which is not raised directly (only
subclasses get raised).  This matches what the docs already said.

a month or two with great success.  Barry may want to tweak it some, but I
think it's a worthwhile enough addition to get some more people trying it
out.

645404).  I'm not 100% sure this is the right fix, so I'll keep the
bug report open for Samuele, but this fixes the index error and passes
the test suite (and I can't see why it *shouldn't* be the right fix
:-).

any_missing() returns less bogus missing modules.

- I've rewritten scan_code() more or less from scratch,
factored bits and pieces out for readability.
- keep track of global assignments and failed imports per
module; use this to determine whether the Y in "from X
import Y" is a submodule or just a global name. This is not
100% doable: you can't tell which symbols are imported when
doing a star import of a non-Python module short of actually
importing it.
- added a new method to ModuleFinder: any_missing_maybe(),
which returns *two* lists, one with certain misses, one with
possible misses. The possible misses are *very* often false
alarms, so it's useful to keep this list separate.
any_misses() now simply returns the union of
any_missing_maybe().

TODO: documentation, test_modulefinder.py

Cleanup whitespace.
Fix unbalanced parenthesis.

docs.  Replaced it with an XXX block, because the hoped-for treatment
of DST endcases remains unclear (Guido doesn't really like raising an
exception when it's impossible to deliver a correct result, but so
far I have no way in hand to consistently deliver a defined incorrect
result either).

we'll simply revert to \mailheader since there's no other good name.

- some minor cleanups

Fix a curly brace that should have been a paren.

Add some times

Document that getatime and getmtime may return floats.