better locale guess for win32

see
https://github.com/tumagonx/pygi-mingw-patches/blob/master/gst-plugins-base-1.4.x.patch

also

https://github.com/tumagonx/pygi-mingw-patches/issues/5

libvips/include/vips/util.h

@@ -332,6 +332,7 @@ guint32 vips__random( guint32 seed );
 guint32 vips__random_add( guint32 seed, int value );
 
 const char *vips__icc_dir( void );
+const char *vips__locale_dir( void );
 
 #ifdef __cplusplus
 }

libvips/iofuncs/init.c

@@ -267,7 +267,6 @@ vips_init( const char *argv0 )
 	char *prgname;
 	const char *prefix;
 	const char *libdir;
-	char name[256];
 
 	/* Two stage done handling: 'done' means we've completed, 'started'
 	 * means we're currently initialising. Use this to prevent recursive
@@ -342,10 +341,7 @@ vips_init( const char *argv0 )
 
 	/* Get i18n .mo files from $VIPSHOME/share/locale/.
 	 */
-	vips_snprintf( name, 256,
-		"%s" G_DIR_SEPARATOR_S "share" G_DIR_SEPARATOR_S "locale",
-		prefix );
-	bindtextdomain( GETTEXT_PACKAGE, name );
+	bindtextdomain( GETTEXT_PACKAGE, vips__locale_dir() );
 	bind_textdomain_codeset( GETTEXT_PACKAGE, "UTF-8" );
 
 	/* Deprecated, this is just for compat.

libvips/iofuncs/util.c

@@ -1969,3 +1969,40 @@ vips__icc_dir( void )
 		(GThreadFunc) vips_icc_dir_once, NULL ) );
 }
 
+#ifdef OS_WIN32
+static HMODULE vips_dll = NULL;
+#ifdef DLL_EXPORT
+BOOL WINAPI
+DllMain( HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved )
+{
+	if( fdwReason == DLL_PROCESS_ATTACH )
+		vips_dll = hinstDLL;
+
+	return( TRUE );
+}
+#endif
+#endif
+
+static void *
+vips_locale_dir_once( void *null )
+{
+	char *prefix;
+
+#ifdef OS_WIN32
+	prefix = g_win32_get_package_installation_directory_of_module( 
+		vips_dll ),
+#else
+        prefix = (char *) g_getenv( "VIPSHOME" );
+#endif
+
+	return( (void *) g_build_filename( prefix, "share", "locale", NULL ) );
+}
+
+const char *
+vips__locale_dir( void )
+{
+	static GOnce once = G_ONCE_INIT;
+
+	return( (const char *) g_once( &once, 
+		(GThreadFunc) vips_locale_dir_once, NULL ) );
+}