tests: stabilize test-blackbox.t on Windows
I didn't look into why the error is more detailed, but that seems like it's a
good thing (other than for recording tests).
--- a/tests/test-blackbox.t Tue Dec 04 00:16:12 2018 -0500
+++ b/tests/test-blackbox.t Tue Dec 04 00:19:33 2018 -0500
@@ -347,7 +347,8 @@
> EOF
$ hg log --debug
removing $TESTTMP/gone/.hg
- warning: cannot write to blackbox.log: $ENOENT$
+ warning: cannot write to blackbox.log: $ENOENT$ (no-windows !)
+ warning: cannot write to blackbox.log: $TESTTMP/gone/.hg/blackbox.log: $ENOTDIR$ (windows !)
$ cd ..
#if chg