input/soup: new input plugin based on libsoup

To demonstrate the new I/O thread.  libsoup is well-integrated into
the GLib main loop, which made this plugin pretty easy to write.

As a side effect, we have to initialize the I/O thread in all debug
programs that use the input API.

configure.ac

@@ -156,6 +156,11 @@ AC_ARG_ENABLE(curl,
 		[enable support for libcurl HTTP streaming (default: auto)]),,
 	[enable_curl=auto])
 
+AC_ARG_ENABLE(soup,
+	AS_HELP_STRING([--enable-soup],
+		[enable support for libsoup HTTP streaming (default: auto)]),,
+	[enable_soup=auto])
+
 AC_ARG_ENABLE(debug,
 	AS_HELP_STRING([--enable-debug],
 		[enable debugging (default: disabled)]),,
@@ -644,6 +649,14 @@ if test x$enable_curl = xyes; then
 fi
 AM_CONDITIONAL(ENABLE_CURL, test x$enable_curl = xyes)
 
+dnl ----------------------------------- SOUP ----------------------------------
+MPD_AUTO_PKG(soup, SOUP, [libsoup-2.4],
+	[libsoup HTTP streaming], [libsoup not found])
+if test x$enable_soup = xyes; then
+	AC_DEFINE(ENABLE_SOUP, 1, [Define when libsoup is used for HTTP streaming])
+fi
+AM_CONDITIONAL(ENABLE_SOUP, test x$enable_soup = xyes)
+
 dnl --------------------------------- Last.FM ---------------------------------
 if test x$enable_lastfm = xyes; then
 	if test x$enable_curl != xyes; then
@@ -1625,6 +1638,7 @@ fi
 
 printf '\nStreaming support:\n\t'
 results(curl,[CURL])
+results(soup, [SOUP])
 results(lastfm,[Last.FM])
 results(mms,[MMS])
 results(cdio_paranoia, [CDIO_PARANOIA])