Support PETSCII terminals connected to non-PETSCII ports

The reported problem (by John "Jay" Crutti) was:
If autodetection of the terminal is used from the defaults menu I get stuck on the prompt to hit my Delete key because on the BBS, it keeps showing me login statistics every time I hit my delete key. 

Add/use new K_CTRLKEYS mode to stop inkey() from handling/eating control-keys (e.g. Ctrl-T) when asking user to hit backspace during defaults->terminal settings.

Allow PETSCII_DELETE (Ctrl-T) as a valid option when asking for the backspace/delete key and set the PETSCII flag in the autoterm variable if hit by the user.