Add declaration for tp_free

Use a saner way to check for non-trivial exception patterns. Not everything has an entry, but everything in a temp probably has a reason for being there.

Prevent calling into CPython with a live exception set while trying to match non-trivial exception patterns in an "except" clause.

Force retranslate Cython modules in "new_build_ext" if "-f" option is passed to "build_ext" command.

Closes #1972.

Multiple inheritance

Previously this was only possible through Python (requring the GIL),
sometimes implicitly (e.g. for string literals).

This fixes #1986.

We should be doing this for pure Python defined classe as well,
but don't have a way to inject it.

Add 'except' values for various function types

[travis] update gcc

Remove direct Unicode hash usage for dict lookups as it proved to be slower after all. Optimising a generic item lookup for dict is faster, though.

See #1979.

Split up the module init function into separate C functions per setup step as it can get fairly lengthy for complex modules, e.g. with many extension types.
This hopefully reduces the function complexity that the C compiler must handle.

Closes #1955.