Parse walltime strings to actual number of minutes
Parse walltime strings to actual number of minutes

Previously, one minute was added, to attempt to deal with
a specific degenerate situation of 0 minutes being specified.

Now, zero minutes will be parsed as 0 minutes, but a warning will
be emitted if the return vales is <1, to nudge the user in the
right direction.

swift-lang/swift-e-lab,Parsl/parsl,Parsl/parsl,swift-lang/swift-e-lab,Parsl/parsl,Parsl/parsl