make opusfile configury to behave with autoconf-2.63 and libtool-1.5.x

diff --git a/configure.ac b/configure.ac
index d68666c..7da0066 100644
--- a/configure.ac
+++ b/configure.ac
@@ -21,7 +21,10 @@ AC_SYS_LARGEFILE
 
 AM_INIT_AUTOMAKE([1.11 foreign no-define dist-zip subdir-objects])
 AM_MAINTAINER_MODE([enable])
-LT_INIT
+
+AC_LIBTOOL_WIN32_DLL
+AC_PROG_LIBTOOL
+#LT_INIT([win32-dll])
 
 m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 
@@ -76,13 +79,13 @@ AM_COND_IF(OP_WIN32,
   AS_IF([test "$enable_http" != "no"],
     AC_CHECK_HEADER([winsock2.h],,
       AC_MSG_WARN([HTTP support requires a Winsock socket library.])
-      enable_http=no
+      [enable_http=no], []
     )
   ),
   AS_IF([test "$enable_http" != "no"],
     AC_CHECK_HEADER([sys/socket.h],,
       AC_MSG_WARN([HTTP support requires a POSIX socket library.])
-      enable_http=no
+      [enable_http=no], []
     )
   )
 )