Clean warnings
Fix a few slab bugs and test
Get Echo tests compiling
Add a unit test for the reactor

Also, change a few APIs that were expecting Sockets, but only actually
depended on IoHandle, to take IoHandle. In general, only APIs that rely
on setsockopts or connection should require Sockets.
ByteBuf - a simple Buf with owned memory
got the lib compiling
re-added Yehuda's unit test
merging in latest from upstream/buf