add cv_ prefix to cached variable.  Remove AC_ARG_PROGRAM as
automake already invokes this. When prefered AC_USE_SYSTEM_EXTENSIONS
exists, use that instead of AC_GNU_SOURCE/AC_AIX/AC_MINUX.
Cleanup socket detection more by creating only a single
SOCKET_LIBS that contains list of all optional libraries
for any socket related funciton.  Make sure that checks
for socket related functions use SOCKET_LIBS when searching.
Check for getopt_long() and getopt.h.  Make OS/2 use
-no-undefined (same as windows).
* ltmain.sh, m4/libtool.m4: Upgrade to libtool 1.5.26.
* Makefile.am: Cleanups to match configure updates.
* frontend/scanimage.c, include/Makefile.in, lib/getopt.c
lib/getopt1.c, toosl/sane-desc.c, include/lgetopt.h:
Rename internal getopt.h to lgetopt.h to allow using
external getopt.h when it exists.  This allows to go
back to optionally compiling getopt()/getopt_long() and its
prototypes and not have conflicts with external headers/symbols.