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).
fixbundle() {
grep -v 'saving bundle' | grep -v 'saved backup' | \
grep -v added | grep -v adding | \
grep -v "unable to find 'e' for patching" | \
grep -v "e: No such file or directory" | \
cat
}