[gimp] Add additional libpng warning flags

[Mukund Sivaraman <muks src gnome org>]

commit 4c26f37611fab83e61fd8575f21d46def755a9f7
Author: Mukund Sivaraman <muks banu com>
Date:   Tue Apr 26 06:49:21 2011 +0530

    Add additional libpng warning flags
    
    This flag warns when we use deprecated API. It's added in configure.ac
    instead of someplace like plugin-defs.pl because libpng is used
    in several places.

 configure.ac |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 2ee8d36..e4c7a1a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1974,6 +1974,12 @@ if test "x$have_pango_1_32" != "xyes"; then
 fi
 
 
+###############################################
+# Enable additional warnings of other libraries
+###############################################
+
+CPPFLAGS="${CPPFLAGS} -DPNG_PEDANTIC_WARNINGS"
+
 ############################
 # Require multihead safe API
 ############################