Mount virtual partitions via new module virtualpartitions.inst, AFTER unsquash.

This avoids overwriting on some virtual /dev devices such as /dev/shm.

Also *FINALLY* fixed that stupid revert bug in partdisks.inst. I'm a moron.
Ship virtualpartitions.inst.
Merge branch 'devel' into debian-devel
debian/linstaller-modules-base.install: ship virtualpartitions.inst.
4.99.5 (RC6)