Disables ASTs in the user program.  ASTs can be disabled during a
     debugging  session  using the command "DISABLE AST", and they can
     be  re-enabled  using  the  command  "ENABLE  AST".   Temporarily
     disabling  ASTs  in  this  fashion  allows  the  user  to prevent
     interrupts from occuring while he is debugging a particular piece
     of code.

 Format

       DISABLE AST

     Example:

     DBG> SHOW AST
     ASTs are enabled
     DBG> DISABLE AST
     %DEBUG-I-DISABLEAST, ASTs were enabled, are now disabled
     DBG> SHOW AST
     ASTs are disabled