pycharm runs old extension, fails to see a new extension

I am building a python extension from a .c file and installing it to site-packages in a virtualenv.  No problem if I run python from a shell, but when I run my test program from PyCharm, it stubbornly uses an old version of the extension package even though I have deleted every copy of the compiled extension file that I can find.  I've tried clearing the cache.  I even tried a new extension with another name, and rebuilt PyCharm's reference to the virtualenv, but still the old extension is used, and the new one is not seen.

I am running PyCharm 2.7.3 on Mac OSX 10.7.5