patchbomb: normalize date format in generated mboxes
mbox format should use time.asctime(). Unfortunately, this function writes
2-characters day of week on Windows while unix one writes a single character.
Normalize to Windows version since the other one can hardly be written with
strftime().
% file replaced with directory
adding a
% should fail - would corrupt dirstate
abort: file 'a' in dirstate clashes with 'a/a'
% directory replaced with file
adding a/a
% should fail - would corrupt dirstate
abort: directory 'a' already in dirstate
% directory replaced with file
adding b/c/d
% should fail - would corrupt dirstate
abort: directory 'b' already in dirstate