Deprecation warning does not blame user code correctly

[mithrandi]

From IRC:

<idnar> …/hypothesis/searchstrategy/deferred.py:81: HypothesisDeprecationWarning: Use hypothesis.strategies.datetimes, which supports full-precision bounds and has a simpler API.
<idnar> that message doesn't actually tell me _what_ is deprecated
<tos9> idnar: It's hypothesis.extras.datetime.datetimes that's deprecated
<tos9> But I think all the warnings are possibly missing a stacklevel
<tos9> because they don't point at the calling code

[Zac-HD]

from hypothesis.extra.datetime import datetimes
datetimes().example()

gives a warning pointing into Hypothesis internals.

However, I think this is due to lazy evaluation rather than a stack error as such; and the proper fix is probably to address the deeper issue of misattributed exceptions in deferred strategy creation.

[Zac-HD]

Nope, turns out it's a lot simpler than that - purely a presentation issue where we should pass stacklevel=2 but currently have stacklevel=3; the traceback is fine but we've told the warnings machinery not to display the relevant frame! Fix incoming 😄