shill: improve logging

- add logging of D-Bus interactions
- convert some error->Populate calls to Error::PopulateAndLog
- slipped in: some whitespace and spelling fixes

BUG=chromium-os:29882
TEST=unit tests

Change-Id: I29cd455cb74cbf467e978a6dc7db3cadac248e43
Reviewed-on: https://gerrit.chromium.org/gerrit/21383
Commit-Ready: mukesh agrawal <quiche@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Tested-by: mukesh agrawal <quiche@chromium.org>
diff --git a/dbus_properties_proxy.cc b/dbus_properties_proxy.cc
index 51b1982..728f806 100644
--- a/dbus_properties_proxy.cc
+++ b/dbus_properties_proxy.cc
@@ -19,6 +19,7 @@
 DBusPropertiesProxy::~DBusPropertiesProxy() {}
 
 DBusPropertiesMap DBusPropertiesProxy::GetAll(const string &interface_name) {
+  SLOG(DBus, 2) << __func__ << "(" << interface_name << ")";
   return proxy_.GetAll(interface_name);
 }