stabletailgraph: add test cases challenging the open merge stack
This adds three more complex test cases with situations requiring tricky
state update in the stack-based iteration (arriving soon).
#require test-repo jshint hg10
$ . "$TESTDIR/helpers-testrepo.sh"
run jshint on all tracked files ending in .js except vendored dependencies
$ cd "`dirname "$TESTDIR"`"
$ testrepohg locate 'set:**.js' \
> 2>/dev/null \
> | xargs jshint