Smarter grouping of differentiable islands
one more test
Merge pull request #1643 from Kenneth-T-Moore/bench

Group differentiable islands in their non-differentiable groups
some cleanup
fixed issue with setting a vtree subvar where another subvar is connected
eliminated the creation of an unnecessary pseudocomp if a src and dest units in a connection have different strings but are really the same unit
a little cleanup
Merge pull request #1644 from naylor-b/vtree_subvar_set

fixed issue with setting a vartree subvar when some other subvar of that vartree is already connected.
Merge pull request #1645 from naylor-b/unitstr

eliminated the creation of an unnecessary pseudocomp if a src and dest ...
a little streamlining
Merge pull request #1646 from naylor-b/algs

some modest performance improvements to the graph stuff
for bret
added wrapper for list_deriv_vars to check return value
Merge branch 'bench' of https://github.com/Kenneth-T-Moore/OpenMDAO-Framework into err_msg
fixed a false positive for non-const indices in expressions
added scalable polynomial problem to openmdao optproblems
Merge pull request #1647 from thearn/dev

added scalable polynomial problem to openmdao optproblems
Merge branch 'err_msg' of github.com:naylor-b/OpenMDAO-Framework into err_msg
Merge pull request #1648 from naylor-b/err_msg

added a wrapper function for list_deriv_vars that checks the return value...
cleanup of list_deriv_vars stuff