use libbio instead of maintaining own buffer
libbio:
always use vlong offsets; die if off_t is too small
R=r
DELTA=163 (23 added, 63 deleted, 77 changed)
OCL=17508
CL=17512
This makes it easy to build with other flags
(like -ggdb) or other compilers (like cc64).
R=r
DELTA=45 (6 added, 22 deleted, 17 changed)
OCL=13790
CL=13793