Ticket #848. Removing the prefix brings "cabal test" in line with other cabal
commands, which do not prefix their output, either. Prior to this patch, the
summary notices which appear before and after each test suite were written to
the temporary log file along with the stdio from the test executable; this would
lead to duplicate notices when the contents of the temporary log file are read
onto the console. After this patch, the summary notices are never written to the
temporary log file, only to the console and the final log file (which is never
read by Cabal), removing the confusing duplicate notices.