The xmlpatterns private headers were not including each other correctly,
making them unusable unless the source directory was available and in
INCLUDEPATH.

Fix it so that the private headers include each other by <private/...>,
allowing them to work for an installed Qt.

Change-Id: I9c7cbad219ed141c356d9ea097e67e0fb2fa550c
Sanity-Review: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jason McDonald <jason.mcdonald@nokia.com>