tests/acceptance: improve default_check_strcmp and add default_check_regcmp
Redmine#3122: acceptance test for list interpolation order
tests/acceptance: s/difference/mismatch/
Merge remote-tracking branch 'tzz/test/3122-list-interpolation-order'

Conflicts:
	tests/acceptance/default.cf.sub
Fix RlistFlatten to preserve order

Close #3122