blackbox: fix exception when logging commands with format characters
When running commands like 'hg export -o mypatch-%N.patch', the blackbox
would throw an exception because it tried to format %N. This change
prevents it from trying to format the command string.
hg debuginstall
$ hg debuginstall
checking encoding (ascii)...
checking Python lib (*lib*)... (glob)
checking installed modules (*mercurial)... (glob)
checking templates (*mercurial?templates)... (glob)
checking commit editor...
checking username...
no problems detected
hg debuginstall with no username
$ HGUSER= hg debuginstall
checking encoding (ascii)...
checking Python lib (*lib*)... (glob)
checking installed modules (*mercurial)... (glob)
checking templates (*mercurial?templates)... (glob)
checking commit editor...
checking username...
no username supplied (see "hg help config")
(specify a username in your configuration file)
1 problems detected, please check your install!
[1]