Change the foreign procedure definitions to use the more portable int
rather than integer-32. Switch to a custom port
[make-custom-binary-input/output-port] rather than a generic port
[make-input/output-port], which resulted in deleting quite a bit of
code. Fix various compiler warnings in the C code, and along the way,
fix a signedness bug in c_write that could have resulted in not writing
the full buffer (but reporting that it did) in the case of errors from
write.
examples/csocket.c, examples/socket.ss
original commit: 9dfa900b251ba480ea13b1796a58d7398146d0b9
