schema doc updated

[Nick Barnes]

I have updated the schema doc to reflect changes since 2.18.1.  I have
also fixed some bugs in the table colouring code.  Please let me know
if you see any serious problems with it.

<http://www.ravenbrook.com/project/p4dti/tool/cgi/bugzilla-schema/>

Note that there have been some pretty major schema changes since 2.18,
so you may find reports which cover a large range of versions are
rather cluttered and confusing.  I welcome suggestions for
improvements, especially to the colouring and annotation which marks
schema changes.

Credit as always is due to Perforce Inc for funding the P4DTI project.

Nick Barnes
P4DTI Project
Ravenbrook Limited