Merge branch '243-really-fix-build-failure-on-ubuntu-16.04' into 'master'

Resolve "cannot build escl backend for Ubuntu 16.04 LTS"

Closes #243

See merge request sane-project/backends!372

acinclude.m4

@@ -630,8 +630,8 @@ for be in ${BACKENDS}; do
       echo "*** $be backend currently requires JPEG library - $DISABLE_MSG"
       backend_supported="no"
     else
-      if test "x${have_jpeg_crop_scanline}" != "xyes" \
-      || test "x${have_jpeg_skip_scanline}" != "xyes"; then
+      if test "x${ac_cv_func_jpeg_crop_scanline}"  != "xyes" \
+      || test "x${ac_cv_func_jpeg_skip_scanlines}" != "xyes"; then
         echo "*** $be backend requires a newer JPEG library - $DISABLE_MSG"
         backend_supported="no"
       fi

configure.ac

@@ -697,7 +697,10 @@ fi
 
 if test "${sane_cv_use_libjpeg}" = "yes"; then
   SANEI_SANEI_JPEG_LO="../sanei/sanei_jpeg.lo"
+  saved_LIBS="${LIBS}"
+  LIBS="${JPEG_LIBS}"
   AC_CHECK_FUNCS(jpeg_crop_scanline jpeg_skip_scanlines)
+  LIBS="${saved_LIBS}"
 fi
 AM_CONDITIONAL(HAVE_JPEG, test x$sane_cv_use_libjpeg = xyes)
 AC_SUBST(SANEI_SANEI_JPEG_LO)