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.