List of things to get fixed (in v2load and dbgcom):
 1) v2load copies the debugger PSP, which references the debugger 16 bit
    environment, thus the argv0 name is wrong.  Fix in si?  Build new
    environment and point to it (with allocated selector?)
 2) CTRL-C attention issues
 3) FPU emulation
 4) Doesn't work under QDPMI 7.5 ?!?
 5) Exception hooks are disabled - would be nice to chain some of them
 6) What if debuggee hooks KBD interrupt?