Add support for zlib during configure

configure.ac

@@ -83,7 +83,24 @@ if test x$jasper = xtrue; then
         )
 fi
 
-
+# check if we want zlib support
+AC_ARG_ENABLE([zlib],
+	[  --enable-zlib    Enable zlib support for deflate compressed DNG files],
+	[case "${enableval}" in
+		yes)	zlib=true ;;
+		no)		zlib=false ;;
+		*)		AC_MSG_ERROR([bad value ${enableval} for --enable-zlib]) ;;
+	esac],[zlib=true])
+
+if test x$zlib = xtrue; then
+	PKG_CHECK_MODULES([ZLIB],[zlib],[
+		CPPFLAGS="$CPPFLAGS $ZLIB_CFLAGS -DUSE_ZLIB"
+		LIBS="$LIBS $ZLIB_LIBS"
+		AC_SUBST([PACKAGE_REQUIRES],[zlib])
+	],
+		AC_MSG_WARN([zlib support cannot be enabled])
+	)
+fi
 
 # check if we want LCMS support
 AC_ARG_ENABLE([lcms],