obshistory: use a more appropriate type for obslog entries
cand is actually a regular changeset and not 'M' (graphmod.MISSINGPARENT). And
'M' is only used for graph edges, but cand is drawn as a graph node.
Visually there's no effect, but the code makes more sense this way.
#require test-repo pyflakes
Copied from Mercurial core (60ee2593a270)
$ cd "`dirname "$TESTDIR"`"
run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)
$ hg locate 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
> | xargs pyflakes 2>/dev/null