Support local variables (tb.tb_frame.f_locals)

I’m sure there’s a reason for this, but it seems that Traceback objects don’t copy the f_locals dictionary from the traceback frame. It would be nice to have this so that, for instance, reraised exceptions can be better introspected in an IDE.

For instance:

>>> def func():
...     a = 1
...    print locals()
...     try:
...         raise ValueError()
...     except Exception as e:
...         exc_type, exc_value, exc_tb = sys.exc_info()
>>> exc_tb.tb_frame.f_locals
{'a': 1, e: ValueError()}
>>> tb = Traceback(exc_tb)
>>> tb.as_traceback().tb_frame.f_locals
{}

There might be something obvious here that I’m missing?

[ionelmc]

f_locals are a can of worms basically, we’d have lots of corner cases like reference loops, unpickleable stuff, overblown pickle result size and such. I’m not saying no but I’m not a fan of the idea either - the primary goal of this library is to be able to display a traceback using stdlib modules (like traceback) from a different process.

[ionelmc]

The changes in #59 made by @marcoffee seem fine to me (some tests needed tho, and some docs explaining that repr will be used, and it can create side-effects). Would those changes solve this/the problems on gevent? I’m not a big gevent user.