partest-only --show-diff does not show diff

[DarkDimius]

[info] !!   3 - run/OrderingTest.scala                    [output differs]
[info] % diff /Users/dark/workspace/dotty/tests/partest-generated/run/OrderingTest-run.log /Users/dark/workspace/dotty/tests/partest-generated/run/OrderingTest.check
[info] ok   4 - run/Course-2002-05.scala
[info] !!   5 - run/Course-2002-03.scala                  [output differs]
[info] % diff /Users/dark/workspace/dotty/tests/partest-generated/run/Course-2002-03-run.log /Users/dark/workspace/dotty/tests/partest-generated/run/Course-2002-03.check
[info] ok   6 - run/Course-2002-04.scala

[DarkDimius]

running with --verbose does not help:

[info] Options: (use partest --help for usage information) run --show-diff --verbose
[info]
[info] Selected 452 tests drawn from 1 named test categories
[info]
[info] # starting 452 tests in run
[info] ok   1 - run/Course-2002-06.scala
[info] !!   2 - run/OrderingTest.scala                    [output differs]
[info] % diff /Users/dark/workspace/dotty/tests/partest-generated/run/OrderingTest-run.log /Users/dark/workspace/dotty/tests/partest-generated/run/OrderingTest.check
[info] ok   3 - run/MutableListTest.scala
[info] !!   4 - run/Course-2002-03.scala                  [output differs]
[info] % diff /Users/dark/workspace/dotty/tests/partest-generated/run/Course-2002-03-run.log /Users/dark/workspace/dotty/tests/partest-generated/run/Course-2002-03.check
[info] ok   5 - run/Course-2002-05.scala

[vsalvis]

--verbose will print the transcript of all failed tests at the end. It does print diffs. I'll investigate why show-diff doesn't work.

[vsalvis]

Fixed --show-diff in #612

@DarkDimius I don't see the interest in having both --show-diff and --verbose, as --verbose will print the diff and also other error output (e.g. compiler output if compilation failed)? So I would suggest removing --show-diff from this PR.