Users now have to call Close() explicitly.  This simplifies using the
class, as most users have automatic socket management already, and
Steal() had to be used often.

Don't let the server care for client problems.

Don't iterate the std::list each time.

Some, or most, Win32 audio players will pass "icy-metadata:1" to
streaming servers. MPD expects a space between ":" and "1" at this
point, and thus does not send any stream metadata. This applies to
foobar2k and Winamp, for example.

According to forums.radiotoolbox.com/viewtopic.php?t=74 not having
a space there is expected behavior, so maybe MPD could accept
both forms to determine if metadata should be sent or not.

Replaces GLib's g_ascii_strncasecmp().

Remove the const_cast from HttpdClient.cxx, and avoid one allocation
in ClientRead.cxx.

Micro-optimization.

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Replaces GLib's GError.