Fix behaviour of commit.
It's now a fatal error if the option to --logfile isn't readable.
Ditto if both --message and --logfile are specified.
port:4:exportport:4:vaportightport:4:import/exportFIXME: history is wrong hereport:1:1:-:eggs:importport:1:2:+:eggs:vaportightport:1:3:+:eggs:import/exportport:0:2:+:spam:exportport:0:1:+:spam:importport:4:import/export