Replace almost all uses of enum connection_state with struct
connection_status. This removes the assumption that errno values used
by the system are between 0 and 100000. The GNU Hurd uses values like
ENOENT = 0x40000002 and EMIG_SERVER_DIED = -308.
This commit is derived from my attachments 450 and 467 to bug 1013.
It seems GnuTLS is not as good at negotiating a supported protocol as
OpenSSL is. ELinks tries to work around that by retrying with a
different protocol if the SSL library reports an error. However,
ELinks must not automatically retry POST requests where some data may
have already reached the server; POST is not a safe method in HTTP.
So instead, collect the name of the TLS-incapable server in a blacklist
when ELinks e.g. loads an HTML form from it; the actual POST can then
immediately use the protocol that worked.
It's a bit ugly that src/network/socket.c now uses
protocol/http/blacklist.h. It might be better to move the blacklist
files out of the http directory, and perhaps merge them with the
BitTorrent blacklisting code.
