Detecting global blocks

[Salvidrim]

Right now users with accounts affected by a global rangeblock of the underlying IP try to appeal via UTRS and get told by the tool that "they are not blocked", which is not accurate information. Either we should allow them through (they can be declined/deferred to meta by responders), or at least there should be an error message explaining the nature of the global block with a link to meta or something.

We've had two cases in the past months that have ended up contacting the mailing list and which I've responded to via e-mail (one result in a vulgar tirade and mailing list ban, the other in a successful IPBE request).