1* Make EXT an independent package, imported from SYS and reexported by this one.
2* Ensure that EXT only contains blessed functions, variables and types
3* Rename the associated C functions so that they get the ext_ prefix instead of si_
4* Eliminate "reexports" from SYS (optional)
The reason for this change is that people have gotten used to referring to SI symbols for functions that are actually not internal, but rather exported and maintained. This includes RUN-PROGRAM, EXTERNAL-PROCESS-PID, etc.
I believe the only problematic part would be step #4