Feature request: empty behavior on assert failure

[rikki cattermole]

In case you don't about this flag:

  -checkaction=[D|C|halt|context]
                     behavior on assert/boundscheck/finalswitch failure

Behavior on assert/boundscheck/finalswitch failure:
   =[h|help|?]    List information on all available choices
   =D             Usual D behavior of throwing an AssertError
   =C             Call the C runtime library assert failure function
   =halt          Halt the program execution (very lightweight)
   =context       Use D assert with context information (when available)