Fix repo --trace to show ref and config loads

The value of the varible TRACE was copied during the import, which
happens before the --trace option can be processed.  So instead we
now use a function to determine if the value is set, as the function
can be safely copied early during import.

Signed-off-by: Shawn O. Pearce <sop@google.com>

trace.py

@@ -0,0 +1,34 @@
+#
+# Copyright (C) 2008 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import sys
+import os
+REPO_TRACE = 'REPO_TRACE'
+
+try:
+  _TRACE = os.environ[REPO_TRACE] == '1'
+except KeyError:
+  _TRACE = False
+
+def IsTrace():
+  return _TRACE
+
+def SetTrace():
+  global _TRACE
+  _TRACE = True
+
+def Trace(fmt, *args):
+  if IsTrace():
+    print >>sys.stderr, fmt % args