Require at least libtool 2.4.2, use LT_INIT

This gives us a few more features and fixes to rely
on which are present in libtool 2.4.2 (released
2011-10-18), which is older than our autoconf,
automake, and gettext requirements.

Update the libtool initialization to use the more
modern (modern in the sense of libtool 1.9b from
2004-08-29) LT_INIT macro.

We still do not use LTDL_INIT() as that insists on
us shipping libltdl sources in our release tarballs.

configure.ac

@@ -225,15 +225,14 @@ GP_VA_COPY
 
 
 dnl check for/set up libtool and libltdl
-dnl AC_DISABLE_STATIC
-dnl AC_DISABLE_SHARED
-dnl AC_LIBLTDL_CONVENIENCE([libltdl])
-dnl AC_WITH_LTDL
-dnl AC_LIB_LTDL
-AC_DISABLE_STATIC 
-AC_LIBTOOL_WIN32_DLL
-AC_LIBTOOL_DLOPEN
-AC_PROG_LIBTOOL
+LT_PREREQ([2.4.2])
+dnl Disable building static library, as no one uses it anyway.
+LT_INIT([
+  disable-static
+  dlopen
+  win32-dll
+])
+dnl LTDL_INIT([external])
 
 dnl We are using our own libltdl checks instead of AC_WITH_LTDL
 dnl because we do not want to ship our own copy of libltdl.

libgphoto2_port/configure.ac

@@ -78,16 +78,14 @@ AM_PROG_AR
 
 
 dnl check for/set up libtool and libltdl
-dnl AC_DISABLE_STATIC
-dnl AC_DISABLE_SHARED
-dnl AC_LIBLTDL_CONVENIENCE([libltdl])
-dnl AC_WITH_LTDL
-dnl AC_LIB_LTDL
+LT_PREREQ([2.4.2])
 dnl Disable building static library, as no one uses it anyway.
-AC_DISABLE_STATIC
-AC_LIBTOOL_WIN32_DLL
-AC_LIBTOOL_DLOPEN
-AC_PROG_LIBTOOL
+LT_INIT([
+  disable-static
+  dlopen
+  win32-dll
+])
+dnl LTDL_INIT([external])
 
 dnl We are using our own libltdl checks instead of AC_WITH_LTDL
 dnl because we do not want to ship our own copy of libltdl.