Not what I came here for, but...

Encoding and decoding are as much a function as handling blobs,
in particular with transcode().

Closes #2870

Addresses the doc part of #2872.

Solaris, (remember Solaris?) will return connection related errnos
on fd metadata operations such as ioctl(2), [gs]etsockopt(2) etc.

We propagated these errors up from VTC_(non)blocking() which could,
theoretically, bail out earlier than it would otherwise have done.
This complicated code far more than it speeded anything up.

Instead just ensure that any errors returned are indeed connection
related, and then ignore them, and let Solaris deal with the broken
connection same way as other operating systems.

This is more complex than it sounds because the active VCL at the
time the topreq got scheduled, may no longer be by the time
the esi:include req gets processed.

Fixes: #2849

again and all the overhead it brought.

Fixes #2846

Fixes #2880

Fixes #2879

but only "errno.h"