Function: getabstime
Section: programming/specific
C-Name: getabstime
Prototype: l
Help: getabstime(): milliseconds of CPU time since startup.
Doc: returns the CPU time (in milliseconds) elapsed since \kbd{gp} startup.
 This provides a reentrant version of \kbd{gettime}:
 \bprog
 my (t = getabstime());
 ...
 print("Time: ", getabstime() - t);
 @eprog
 For a version giving wall-clock time, see \tet{getwalltime}.
