Merge lp://staging/~unity-api-team/indicator-network/lp1411714-14.09 into lp://staging/indicator-network/14.09

* Guard access to ofono::Modem properties that have a
  shared_ptr inside them with a mutex.
* simplify GMainLoopDispatcher

The crash was caused by a memory corruption caused by a threading issue.
One example http://pastebin.ubuntu.com/9805338/

    on frame #20 after the control leaves Modem::Private::update()
    the stack is unwinded which results in destructor of SimManager
    to be called on frame #11, although the simmgr shared_ptr inside
    update() appears to be empty (points to 0x0) and the destuctor for
    the SimManager object has already been ran once.

The cause of the corruption is explained here:
http://cppwisdom.quora.com/shared_ptr-is-almost-thread-safe

org::ofono::Interface::Modem has two core::Properties that contain shared_ptr:

    core::Property<NetworkRegistration::Ptr> networkRegistration;
    core::Property<SimManager::Ptr> simManager;

Core::Property<T> defines:

  private:
    mutable T value;

Which in SimManager's case for example becomes:

    mutable std::shared_ptr<SimManager> value;

Core::Property<T> defines the get() and set() as:

    inline virtual const T& get() const
    {
        if (getter)
            mutable_get() = getter();

        return value;
    }

    inline virtual void set(const T& new_value)
    {
        if (value != new_value)
        {
            value = new_value;

            if (setter)
                setter(value);

            signal_changed(value);
        }
    }

Now, in indicator-network we have two threads running:

    thread 1: worker thread for dbus-cpp
    thread 2: thread that runs GMainLoop

As an example the corruption happens when thread 1 does in ofono.h:
    simManager.set(std::shared_ptr<SimManager>());

and at the same time thread 2 does in modem.cpp:
    auto simmgr = d->m_ofonoModem->simManager.get();

set() writes to core::Property::value in one thread while get() reads the value from another simultaneously.

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The situation is fixed in this MP by guarding the read and write to the properties by a mutex org::ofono::Interface::Modem::_lock.

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This MP also simplifies the locking around GMainLoopDispatch as the original code was seen as error prone regarding of locking.