ltdl, remove unsusd check for ltdl.h
ltdl, move SXE_CHECK_LIBLTDL to configure.ac

autoreconf likes to see this in configure.ac. Most important It failed to
recongnice the LTDL_INIT mode, which is needed to guess the right
libtoolize options.

Signed-off-by: Sebastian Freundt <freundt@fresse.org>

Conflicts:
	configure.ac
ltdl, use LTDL_INIT's "recursive" mode

This decreases the distdir size about 1.3 MB and increases configure
speed.

Signed-off-by: Sebastian Freundt <freundt@fresse.org>

Conflicts:
	configure.ac
ltdl, workaround libtool LT_CONFIG_H bug

Building embedded libltdl fails because config.h is located in
subdir src. See libtool bug #12262
http://lists.gnu.org/archive/html/bug-libtool/2012-08/msg00007.html

Signed-off-by: Sebastian Freundt <freundt@fresse.org>

Conflicts:
	configure.ac
chore, put at least half the ugly bits to ltdl initialisation into SXE_CHECK_LIBLTDL

Older libtools want LTDL_INIT and LT_CONFIG_LTDL_DIR in c.ac.
See https://github.com/hroptatyr/uterus/pull/1#issuecomment-16110043

Signed-off-by: Sebastian Freundt <freundt@fresse.org>

Conflicts:
	configure.ac
Merge branch 'bld/ltdl' into next

* bld/ltdl:
  chore, put at least half the ugly bits to ltdl initialisation into SXE_CHECK_LIBLTDL
  ltdl, workaround libtool LT_CONFIG_H bug
  ltdl, use LTDL_INIT's "recursive" mode
  ltdl, move SXE_CHECK_LIBLTDL to configure.ac
  ltdl, remove unsusd check for ltdl.h