auth: fixup prompt and fail substitution

[PaideiaDilemma]

This PR brings back fingerprint errors in $FAIL. That was regressed by #603.

BREAKING:

• Removed $PROMPT variable. Either use $PAMPROMPT or $FPRINTPROMPT.
• Removed $FPRINTMESSAGE. Use $FPRINTPROMPT instead. There is also
  $FPRINTFAIL.

[PaideiaDilemma]

After pondering with @alba4k we thought removing PROMPT was appropriate, since it is not that useful and we don't need to solve the "when to show which auth prompt" problem.

$FAIL and g_pAuth->getLastFailText() are now handled by the auth method directly (they specify the failText via g_pAuth->enqeueFail.

[PaideiaDilemma]

@vaxerski this one is ready.

Regarding the breaking variable changes (PROMPT & FPRINTMESSAGE), i could instead:

• not remove them yet and say they will be removed in a future release in the wiki
• replace them with a message to the user. smth like $PROMPT is Depreciated!

Let me know if you think any of those make more sense.
Personally i think not many people use those vars, so i think it is not that big of a problem.

[alba4k]

I think they can be safely be removed, but if you really want to be safe the easiest solution is probably to just keep them working for a while and print a warning to stderr saying that the variable is deprecated and will be removed soon.

[vaxerski]

why do the breaking changes? is there any good reason?

[alba4k]

FPRINTMESSAGE is a misleading name, FPRINTFAIL is more consistent with the other variables and explains the purpose of the variable better

a unified PROMT variable doesn't really make sense with more than one auth method. Separating the variables makes more sense and gives the user more control

[vaxerski]

thanks. Wiki mr?

[vaxerski]

oops, already there.