I wasn't sure where to obtain crew, but I installed
http://www.selenic.com/mercurial-snapshot.tar.gz ('mercurial-3b081f2a77b2') and
now receive:

$ hg debuginstall
Checking encoding (ISO8859-1)...
Checking extensions...
Checking templates...
Checking patch...
Checking merge helper...
automatic merge failed! Exiting.
merge failed
 Got unexpected merge error 256!
 Got unexpected merge results!
 (your merge helper may have the wrong argument order)
 Result: '1\n2\n3\ninsert\n4\n'
Checking commit editor...
Checking username...
2 problems detected, please check your install!