Genie:  Fix SheepShaver driver check

The check for the Display_Video_Apple_Sheep driver correctly detects the
current case of the leading dot being missing, but the logic intended to
future-proofedly catch a hypothetical corrected driver name (with dot in
place) is erroneously comparing the string's length byte to '.', not the
first character.
Genie:  Axe unused UnitTable_Container
mac-types:  Add AuxDCE
mac-sys-utils:  Add unit_table unit
Genie:  Use mac-sys unit_table in /sys/mac/vol
Genie:  Remove volume_is_ram_disk::applies() guard
Genie:  Use mac/sys/unit_table in sys/mac/errata
Genie:  Use mac-sys unit_table in /sys/mac/unit
Genie:  Cull unneeded includes in sys/mac/unit.hh
Genie:  Compile sys/mac/unit.cc even for Carbon
Merge branch 'unit_table'

Reduce Genie's preprocessing footprint by several megabytes.