Minor fixes, improvements and nitpicks

Fixes:

• Incorrectly escaped regex everywhere: .ini -> \.ini

Improvements:

• Print out git submodule commits using one-liner. Existing practice of hacking up program output breaks when switching languages, so don't do it.

  $ LANG=fr_FR ./MakefileSyncCommand

• Better exit code convention: 1=aborted; 2=error

Nitpicks:

• Interpolated variables instead of dot-gluing strings everywhere
• Use better regex delimiters
• Fail faster if ini_sync.yaml isn't found.