Removed VMS support.

This is due to the lack of a working build script for VMS.
Updated CHANGES file.
Performed a change that I forgot from 1f2d6d1e0116.

The CHANGES file mentioned the existence of a file called
Jamfiles/DefaultJambase. I forgot to rename the mentioned file; this is
now fixed.
The jambase.c file is now automatically generated.
Updated CHANGES file.