support machines where unsigned long is 4 bytes

[Martin Albrecht]

Currently we get:

dgs/dgs_misc.h: In function '_dgs_randomb_libc':
dgs/dgs_misc.h:82:122: warning: left shift count >= width of type [-Wshift-count-overflow]
   unsigned long pool = (((unsigned long)random()) << 0) ^ (((unsigned long)random()) << 22) ^ (((unsigned long)random()) << 44);