tests: add tests for showing stack when merge is involved This patch adds tests of showing stack when merges are involved. This will help us in changing the behaviour and realising that in later patches.

syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes