ftp: Allow other locations of netrc file.

Introduce a command line option and an environment
variable to override the legacy location $HOME/.netrc.
build: fix syntax-check
ftp: Hash command semantic.
Handle access times in sub-seconds.

Use contemporary and resonably portable techniques
for microsecond or better accuracy in `struct stat'.
Portability of canonical host name.

For a numerical host name, getaddrinfo() need not set
a value for `ai_canonname'.  Protect against this.
Problem was uncovered by a system running OpenBSD 5.5.
libls: Inconsistent options.
whois: Cooperate with misbehaving servers.

When the socket is half-closed by the client, then some
remote servers abort connection without a complete reply.
The cause was located and reported by Alexander Zubkov.
Fix sc_require_config_h