* PollVec.cc, PollVec.h: (FDSetNotReady) new method.
fixed buffer size setting when rate is unlimited
(SetNotReady) new method.
don't call Do; use SetNotReady to skip repeated read() calls.
use buffer-size=0x10000, as it seems optimal even for local transfers.
(For some reason Linux kernel cannot pass 0x20000 bytes over local sockets,
is passes it as two portions of data: 131072+68); don't loop over _LL functions.