suzerain: #2983 #3070 back to symbolic inverse

Motivated by compile-times and it seemingly making no
real difference in behavior, returning to the symbolic
inverse computation.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44850 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: use "half" more consistently

Not real important here, but will be nicer for copy'n'paste
work for anyone who comes afterward for symbolic purposes.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44851 0bd85f0b-c151-43b9-a1e9-27231104551f