use pre-instantiated identifier string when looking up or setting the vtable of exported/imported extension types

handle some more cases where the error status is known to be used and clean up 'unraisable exception' code

Autodoc improvements

Regression test for #42.

Add strspn to string.pxd

Fixed .srctree tests execution

fix compiler crash on bad code (complex % x) and move directive handling in ModNode to analysis phase

Removed the warning about docstrings for private attributes. Fixed erroneous docstring recognition past the blank line.

Resolve depends attribute with respect to include_dirs.