Land patch for sgk@chromium.org:
Land patch for sgk@chromium.org:

Don't copy the ENV variable from the users's external environment into
construction environments.  SCons uses this as a dictionary of environment
values for the commands it executes.

BUG=none
TEST=build with the variable ENV set in the user environment

Review URL: http://codereview.chromium.org/173294

git-svn-id: b158db1e4b4ab85d4c9e510fdef4b1e8c614b15b@2750 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh