Bug 1083279 - Part 2: Allow SCRIPT_DIRECTORY to depend on the invocation script name. r=ted

This issue manifests itself as the reftest extension not being installed
for local testers.  This is because the extension's location is
determined relative to SCRIPT_DIRECTORY, and for local testers, __file__
ignores the symlink from $OBJDIR/_tests/reftest/runreftest.py ->
$SRCDIR/layout/tools/reftest/runreftest.py.

This was changed in Bug 915865.

layout/tools/reftest/runreftest.py

@@ -19,7 +19,7 @@ import sys
 import tempfile
 import threading
 
-SCRIPT_DIRECTORY = os.path.abspath(os.path.realpath(os.path.dirname(__file__)))
+SCRIPT_DIRECTORY = os.path.abspath(os.path.realpath(os.path.dirname(sys.argv[0])))
 sys.path.insert(0, SCRIPT_DIRECTORY)
 
 from automationutils import (