It turns out that the ascii data source validator is
not thread safe, so it needs to be protected with a
mutex.
This was discovered in the process of making the
vector dialog mode sticky.

Handle data sources which are temporarily typed into the
data source selector, but which are not actually used.
-Delete them when another source is selected
-Delete them if the window is closed
-Delete them if a non-dataobject is created instead.

Additionally, when a data source is deleted, delete its slave
primitives as well.

(See http://marcmutz.wordpress.com/effective-qt/prefer-to-use-normalised-signalslot-signatures)

…heck them

Setting -DQT_STRICT_ITERATORS allows catching unwanted detaching
when using begin() on Qt container which isn't const.