Manav's proposed "fix" for UnsteadySolver AMR
Correct fix for UnsteadySolver::reinit()

Looks like Manav identified a real bug which just hadn't been hit by
the particular way my own AMR/transient loops interleaved.  His
original fix could have introduced a new problem in other corner
cases, but this reduced fix seems to handle the bug triggered by his
app but shouldn't add any new bugs in others' apps.
Merge pull request #61 from roystgnr/manav_unsteady

Manav's and my fix for an UnsteadySolver+AMR failure