Rework the http code to require poll() only when really needed.

Rework the http code to require poll() only when really needed.
Especially tls_read() and tls_write() do not map 1:1 to read() and write()
calls and so assuming that after a tls_read() one needs to poll for more
data is wrong. Instead call tls_read() until it returns a TLS_WANT_*
return.

While here also ignore SIGPIPE. It is almost impossible to properly guard
from SIGPIPE by looking at POLLHUP. Instead just let write() handle it and
return an error.

Putting this in now so this can be tested widely.