Function: factorint
Section: number_theoretical
C-Name: factorint
Prototype: GD0,L,
Help: factorint(x,{flag=0}): factor the integer x. flag is optional, whose
 binary digits mean 1: avoid MPQS, 2: avoid first-stage ECM (may fall back on
 it later), 4: avoid Pollard-Brent Rho and Shanks SQUFOF, 8: skip final ECM
 (huge composites will be declared prime)

