Return exit codes for specific failures when in non-interactive mode

[grantemsley]

Fixes #1116

When in non-interactive mode (exitonfailure is enabled), returns distinct exit codes for some of the known failures.

This will let users handle them differently in their scripts. For example I have a script that restart the console client if it's killed or crashes. Right now I do something like this:

:start
MinecraftClient.exe
timeout /t 60
goto start

Now I can do this:

:start
MinecraftClient.exe
if '%ERRORLEVEL%'=='4' goto loginfailed
timeout /t 60
goto start

:loginfailed
echo 'Login failure. Stopping.'
pause

Doing this should avoid hammering the authentication servers with a bad password, and prevent getting IP blacklisted as easily.

[ORelio]

Seems good to me. Thanks for your contribution!