- previously used a Pstream::exit() invoked from the argList
destructor to handle all MPI shutdown, but this has the unfortunate
side-effect of using a fixed return value for the program exit.
Instead use the Pstream::shutdown() method in the destructor and allow
the normal program exit codes as usual. This means that the
following code now works as expected.
```
argList args(...);
if (...)
{
InfoErr<< "some error\n";
return 1;
}
```
- resets the output buffer completely - implementing what rewind was
likely meant to have accomplished for many use cases.
STYLE: OSHA1stream reset() for symmetry. Deprecate rewind().