Motivation / Problem

When regression test fails, sometimes our basic diff is not the most usable output. Especially when you are adding more checks to regression test. Having the output in a file can allow use of more avanced tools to compare it with expected output.

Description

On failure simply save the output to a file.
But first I needed to add support for more output lines than expected.
And while in the area I moved the counter increment before diff output, so lines are numbered from 1.

Limitations

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • PR must be added to API tracker