QT4/pre-build: installing the examples needs the source tree

When installing the examples, this package cannot be used in its pre-build
archive form. But else it can. So disable this feature only on demand.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>
Mono/pre-build: targetinstall needs access to the source tree

Installing the mscorlib.dll needs the access to the source tree, so this
package cannot be used in its pre-build archive form.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>
bluez/pre-build: installing the test scripts needs the source tree

When installing the test scripts, this package cannot be used in its
pre-build archive form. But else it can. So disable this feature only
on demand.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>
PTXdist: be more helpful using the pre-build archive feature

To make use of this helpful PTXdist feature, help a new user to understand
how to configure her/his project.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>