ABCL fixes

Hi, so after tracing a good amount of time I found the reasons for two problems on ABCL, but really any other implementation using BIOs as well.

First, the `*SOCKET*` variable should be the underlying socket, not the stream itself.

Second, `WITH-POINTER-TO-VECTOR-DATA` on ABCL *copies* the data only after the body executed, so retrieving the read bytes afterwards is necessary to read the correct bytes. It isn't harmful on platforms like SBCL where the data is mapped directly, so I guess it's safe to apply, also assuming that fixing that in CFFI on ABCL will take a bit of time.