http: use libcurl

MPD's HTTP client code has always been broken, no matter how effort
was put into fixing it.  Replace it with libcurl, which is known to be
quite stable.  This adds a fat library dependency, but only for people
who need streaming.

configure.ac

@@ -102,6 +102,17 @@ AC_ARG_ENABLE(un,
 	[enable_un=yes])
 
 
+dnl
+dnl input options
+dnl
+
+AC_ARG_ENABLE(curl,
+	AS_HELP_STRING([--disable-curl],
+		[enable support obtaining song data via HTTP (default: enable)]),
+	[enable_curl=$enableval],
+	[enable_curl=yes])
+
+
 dnl
 dnl audio output plugins
 dnl
@@ -316,6 +327,13 @@ case $host in
 		enable_osx=yes ;;
 esac
 
+if test x$enable_curl = xyes; then
+	PKG_CHECK_MODULES(CURL, [libcurl],
+		AC_DEFINE(HAVE_CURL, 1, [Define when libcurl is used for HTTP streaming]),
+		enable_curl=no)
+fi
+AM_CONDITIONAL(HAVE_CURL, test x$enable_curl = xyes)
+
 if test x$enable_shout_ogg = xyes || x$enable_shout_mp3 = xyes; then
 	enable_shout=yes
 	PKG_CHECK_MODULES([SHOUT], [shout],