STR 1949 - revise configure.in to cerrectly detect png_set_tRNS_to_alpha

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@6504 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

configure.in

@@ -578,7 +578,7 @@ AC_CHECK_LIB(z,gzgets,
 
 AC_ARG_ENABLE(localpng, [  --enable-localpng       use local PNG library, default=auto],
     [if test x$enable_localpng = xyes; then
-	ac_cv_lib_png_png_set_tRNS_to_alpha=no
+	ac_cv_lib_png_png_set_tRNS_to_alpha=yes
     fi])
 
 AC_CHECK_LIB(png,png_set_tRNS_to_alpha, [
@@ -586,13 +586,16 @@ AC_CHECK_LIB(png,png_set_tRNS_to_alpha, [
     PNG=""
     IMAGELIBS="-lpng $IMAGELIBS"
     AC_DEFINE(HAVE_LIBPNG)
-    AC_CHECK_HEADER(png.h, AC_DEFINE(HAVE_PNG_H))],[
+    AC_DEFINE(HAVE_PNG_GET_VALID)
+    AC_DEFINE(HAVE_PNG_SET_TRNS_TO_ALPHA)    AC_CHECK_HEADER(png.h, AC_DEFINE(HAVE_PNG_H))],[
     if test x$enable_localpng = xno; then
         PNGINC=""
         PNG=""
     else
 	AC_DEFINE(HAVE_LIBPNG)
         AC_DEFINE(HAVE_PNG_H)
+        AC_DEFINE(HAVE_PNG_GET_VALID)
+        AC_DEFINE(HAVE_PNG_SET_TRNS_TO_ALPHA)
         PNGINC="-I../png"
         PNG="png"
         IMAGELIBS="-lfltk_png $IMAGELIBS"