util: add gitversion utility for stamping standalone jars.

gitversion provides a replacement for svnversion now the source code
is managed by git.  The git show/describe commands don't seem to do
quite what is required, so this is a short shell script that does.
It is used to replace svnversion in the ttools and topcat
build-standalone targets to place fixed version strings into the
published jar files which can report build versions at runtime.
ttools: fix meta mode for array-valued table parameters.

Previously mode=meta just did a toString() on arrays, now it
outputs each element as a different line to stdout.
topcat: better display of aux column metadata.

Non-standard per-column "auxiliary" metadata is now displayed better,
in particular if the aux metadata type is array-valued the array
elements are shown rather than just calling toString() on the array object.
It's not perfect though; if the aux metadata type is Object (because
different columns have values of different types) it will still revert to
the old behaviour.  This case is unusual, but not unheard of.