[petsc-dev] PetscOptions defaults after PetscInitialize

[Jed Brown]

For users that read their own configuration files and/or choose
PetscOptionsInsertFile after PetscInitialize, we don't have a good way
to avoid overwriting PETSC_OPTIONS or command-line options.  The user
could manually find argv and the environment variable, but that's a poor
abstraction.  Should PetscOptionsInsertFile learn how to behave so as to
add new entries to the options database, but not supersede any that
already exist?