graphics/gthumb: prepare for exiv2-0.27

Import gentoo's (via mageia) patch:
https://gitweb.gentoo.org/repo/gentoo.git/tree/media-gfx/gthumb/files/gthumb-3.6.2-exiv2-0.27.patch?id=a430106ef87cdbffc6cefbc1ac1a8e5bb3ea6242

PR:		235943

graphics/gthumb/Makefile

@@ -4,7 +4,7 @@
 
 PORTNAME=	gthumb
 PORTVERSION=	3.6.1
-PORTREVISION=	4
+PORTREVISION=	5
 CATEGORIES=	graphics
 MASTER_SITES=	GNOME
 DIST_SUBDIR=	gnome3

graphics/gthumb/files/patch-gentoo_2bd8b9

@@ -0,0 +1,34 @@
+Patch kindly borrowed from Mageia.
+
+* asturm@gentoo.org: Dropped unnecessary and backwards incompatible
+xmp_exiv2.hpp include.
+
+https://gitlab.gnome.org/GNOME/gthumb/issues/30
+
+diff -Nru a/extensions/exiv2_tools/exiv2-utils.cpp b/extensions/exiv2_tools/exiv2-utils.cpp
+--- extensions/exiv2_tools/exiv2-utils.cpp	2018-06-17 08:24:44.000000000 +0200
++++ extensions/exiv2_tools/exiv2-utils.cpp	2018-12-31 15:51:50.912329232 +0100
+@@ -32,7 +32,7 @@
+ #include <sstream>
+ #include <vector>
+ #include <iomanip>
+-#include <exiv2/xmp.hpp>
++#include <exiv2/exiv2.hpp>
+ #include <gthumb.h>
+ #include "exiv2-utils.h"
+ 
+@@ -1073,7 +1073,11 @@
+ 
+ 	try {
+ 		if (exifData.empty()) {
++#if EXIV2_TEST_VERSION(0,27,0)
++			throw Exiv2::Error(Exiv2::kerErrorMessage, " No Exif data found in the file");
++#else
+ 			throw Exiv2::Error(1, " No Exif data found in the file");
++#endif
+ 		}
+ 		Exiv2::ExifData::const_iterator end = exifData.end();
+ 		for (Exiv2::ExifData::const_iterator i = exifData.begin(); i != end; ++i) {
+
+
+