Make protobuf build

This includes the following:
  - Setting up dependencies protobuf needs
  - A few hacks to make protobuf work with our version of Bazel (going
    to upgrade soon...)
  - A few tweaks to make protobuf be happy in third_party
  - Commenting out a few things we don't care about that didn't want to
    work

Tested with -c fastbuild for all 3 toolchains.

Change-Id: I02c50cd7e82e509bd7973f2e7cecf9b7d183783e
diff --git a/third_party/python_import_helpers.BUILD b/third_party/python_import_helpers.BUILD
new file mode 100644
index 0000000..38a68ec
--- /dev/null
+++ b/third_party/python_import_helpers.BUILD
@@ -0,0 +1,19 @@
+# This repository is used to create helper __init__.py files which import things
+# under third_party at the root of the Python import namespace instead of
+# requiring third_party.xyz. in front of them.
+
+genrule(
+  name = 'google_protobuf_importer_init',
+  outs = ['google/__init__.py'],
+  cmd = 'echo "%s" > $@' % '\n'.join([
+    'import sys',
+    'import third_party.protobuf.google.protobuf',
+    'sys.modules[\'google.protobuf\'] = third_party.protobuf.google.protobuf',
+  ]),
+)
+
+py_library(
+  name = 'google_protobuf_importer',
+  visibility = ['//visibility:public'],
+  srcs = [':google_protobuf_importer_init'],
+)