figure out why MM's and FS's buildslaves are red on some steps

[zooko]

MM's buildslave "MM netbsd5 i386 warp" fails the test-from-egg step, like this:

Traceback (most recent call last):
  File "/home/tahoe/buildslave/tahoe/netbsd5-i386/build/misc/build_helpers/run_trial.py", line 52, in <module>
    __import__(modulename)
ImportError: No module named allmydata.test

FS's buildslave "FreeStorm Win7-amd64-mingw py2.6" fails the test-with-fake-pkg step, like this:

Traceback (most recent call last):
  File "c:\buildbot_tahoe\FreeStorm_Win7-amd64-mingw_py2.6\build\src\..\misc\build_helpers\run_trial.py", line 98, in <module>
    raise AssertionError(msg)
AssertionError: We seem to be testing the code at 'c:\\python26\\lib'
(according to the source filename 'c:\\python26\\lib\\site-packages\\allmydata\\test\\test_base62.pyc'),
but expected to be testing the code at 'c:\\buildbot_tahoe\\freestorm_win7-amd64-mingw_py2.6\\build'.
This script needs to be run from the source directory to be tested.

(In ​a subsequent build, this buildslave ​hung, and then in subsequent builds it was ​unable to start due to a process holding a handle to the build directory.)