Install GObject properties during class_init

See https://bugzilla.gnome.org/show_bug.cgi?id=701196

Add a new hash table utility wrapper which hashes GSize; on x32
it falls back to malloc().

Use this to keep track of properties to be installed; our
generic class_init function looks them up based on GType.

V2: Don't use a callback, just pass property array to
    register_type().  Keep signal installation where it
    is for now, since passing that down too would require
    a new structure type.

https://bugzilla.gnome.org/show_bug.cgi?id=701196