Bug 1277087 - Change how the buildconfig module searches for config.status. r=gps

So far, we relied on the module being copied over in the virtualenv, and
the module itself would try to find config.status in parent directories
of its own location. Unfortunately, this falls short when the source
tree's build/ directory appears early in the sys.path.

With this change, we don't copy the module to the virtualenv anymore,
and try to find config.status in parent directories of the python
executable, which, when running from the virtualenv, will be equivalent
to the current behavior.

build/buildconfig.py

@@ -6,7 +6,7 @@ import imp
 import os
 import sys
 
-path = os.path.dirname(__file__)
+path = os.path.dirname(sys.executable)
 while not os.path.exists(os.path.join(path, 'config.status')):
     parent = os.path.normpath(os.path.join(path, os.pardir))
     if parent == path:

build/virtualenv_packages.txt

@@ -23,7 +23,6 @@ mozilla.pth:dom/bindings
 mozilla.pth:dom/bindings/parser
 mozilla.pth:layout/tools/reftest
 moztreedocs.pth:tools/docs
-copy:build/buildconfig.py
 packages.txt:testing/mozbase/packages.txt
 objdir:build
 gyp.pth:media/webrtc/trunk/tools/gyp/pylib