vboxwrapper.cpp

Vboxwrapper detects known buggy versions of Vbox and calls
boinc_temporary_exit().
The "Incompatible version" message appears in the task status
in the BOINC Manager, where some users may never see it.
It needs to appear as a notice, telling the user to upgrade VBox.

To do this, I added an optional argument to boinc_temporary_exit()
saying that the message should be delivered as a notice.
This is conveyed to the client by adding
a line containing "notice" to the temp exit file.
I changed the client and vboxwrapper to use this.