Various buildbots show a failure on test_heapq.

 * "x86 FreeBSD 3.x" failed on revision r83882 (r83869 was OK)
   http://www.python.org/dev/buildbot/all/builders/x86%20FreeBSD%203.x/builds/492
   and next runs were OK, too

 * "PPC (Leopard|Tiger) 3.x" and "x86 Tiger 3.x" fail consistently from r83889 onwards.

 * all "gentoo 3.x" and "Ubuntu 3.x" fail on r83981
   http://www.python.org/dev/buildbot/all/builders/x86%20gentoo%203.x/builds/2816
   http://www.python.org/dev/buildbot/all/builders/x86%20Ubuntu%203.x/builds/1707

This is a variant of the kind of annoyance pointed out in #9548. Here, it seems addbuilddir() in Lib/site.py shouldn't import sysconfig, because it imports the re module.

For some reason, sys.modules['heapq'] contains the Python implementation instead of the C implementation.

Tested with r83981 on python 3:

Python 3.2a1+ (py3k:83981M, Aug 13 2010, 19:02:31) 
[GCC 4.3.4] on linux2
Type "help", "copyright", "credits" or "license" for more information.

>>> import heapq
>>> heapq.heappop(10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/florent/dev/python/py3trunk/Lib/heapq.py", line 140, in heappop
    lastelt = heap.pop()    # raises appropriate IndexError if heap is empty
AttributeError: 'int' object has no attribute 'pop'

>>> import _heapq
>>> _heapq.heappop(10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: heap argument must be a list


These tests (TestErrorHandling) are supposed to run with the C module only.

Here is a patch which works if the patch in #9548 is also applied.
It won't work alone because opening a file in text mode currently imports locale which imports re, etc. ... all before adding the build dir to sys.path.

Of course, since the logic in addbuilddir() is now much simpler, it could also be rewritten in C somewhere (where?), and the launched much earlier during the startup phase.

Here is a C version of addbuilddir. It solves the present issue.

I've committed an updated version of the C patch in r83988, after Victor's comments on IRC.

r83988 is also the correct fix for #586680: I updated this issue.