New rpcclient command "at" for NT scheduler control, a slightly improved

New rpcclient command "at" for NT scheduler control, a slightly improved
version of the NT command.

at { time [/INTERACTIVE] [{/EVERY|/NEXT}:5,Sun,...] command | [/DEL] [jobid] }

Examples (options used in abbreviated form):
at                                         ; Shows all jobs
at 1                                       ; Detail on job 1
at /D                                      ; Deletes all jobs
at /D 1                                    ; Deletes job 1
at 11:11:11AM /I /N:1 d:\humour\silly.exe  ; First of next month
at 9:00AM /E:M,T,W,Th,F net send MATTY Hi  ; Each weekday
at 11:00PM /E c:\winnt\backup.exe          ; Every day
(This used to be commit cf8c476d2eec24c150877b6bb8af7f7875cc1840)