[qtcontacts-sqlite] Ensure incidental contact is linked into aggregate

Previously, if a single write caused both a modify of an existing
synctarget constituent plus the creation of a new incidental contact,
the incidental contact would not be linked into the appropriate
aggregate via a relationship.
This commit ensures that the incidental contact is always linked
correctly.
Merge pull request #115 from chriadam/fixincidental

[qtcontacts-sqlite] Ensure incidental contact is linked into aggregate