configure, app: encourage packagers to set custom bug tracker.

We get a lot of packaging bugs for third-party builds in our tracker,
especially since our debug tool now opens directly our bug tracker.
It would be preferred if third-party packagers were to make a first
filtering of bugs and only reported once they knew for sure that the bug
is in core code, and not in packaging.

Our configure script will now propose a --with-bug-report-url option
allowing to set a different web address. This address will be the one
opening in the debug dialog.

app/widgets/gimpcriticaldialog.c

@@ -329,14 +329,23 @@ gimp_critical_dialog_response (GtkDialog *dialog,
     case GIMP_CRITICAL_RESPONSE_URL:
       {
         const gchar *url;
+        gchar       *temp = g_ascii_strdown (BUG_REPORT_URL, -1);
+
+        /* Only accept custom web links. */
+        if (g_str_has_prefix (temp, "http://") ||
+            g_str_has_prefix (temp, "https://"))
+          url = BUG_REPORT_URL;
+        else
+          /* XXX Ideally I'd find a way to prefill the bug report
+           * through the URL or with POST data. But I could not find
+           * any. Anyway since we may soon ditch bugzilla to follow
+           * GNOME infrastructure changes, I don't want to waste too
+           * much time digging into it.
+           */
+          url = PACKAGE_BUGREPORT;
+
+        g_free (temp);
 
-        /* XXX Ideally I'd find a way to prefill the bug report
-         * through the URL or with POST data. But I could not find
-         * any. Anyway since we may soon ditch bugzilla to follow
-         * GNOME infrastructure changes, I don't want to waste too
-         * much time digging into it.
-         */
-        url = "https://bugzilla.gnome.org/enter_bug.cgi?product=GIMP";
         browser_open_url (url, NULL);
       }
       break;

configure.ac

@@ -2312,6 +2312,34 @@ else
 fi
 AM_CONDITIONAL(HAVE_DESKTOP_FILE_VALIDATE, test "x$DESKTOP_FILE_VALIDATE" != "xno")
 
+####################
+# Set bug report URL
+####################
+
+# Allowing third-party packagers to set their own bugtracker URL, in
+# order to filter first packaging bugs from core bugs.
+
+AC_ARG_WITH(bug-report-url,
+            [  --with-bug-report-url           URL used by the debug dialog to report bugs],,
+            [with_bug_report_url="$PACKAGE_BUGREPORT"])
+
+if test "x$with_bug_report_url" = "x"; then
+  with_bug_report_url="$PACKAGE_BUGREPORT"
+fi
+
+AC_DEFINE_UNQUOTED(BUG_REPORT_URL, "$with_bug_report_url",
+                   [The URL to open in order to report bugs])
+
+override_bug_report_url=
+if test "x$with_bug_report_url" = "x$PACKAGE_BUGREPORT"; then
+override_bug_report_url="
+NOTE: if you plan on packaging GIMP for distribution, it is recommended
+      to override the bug report URL with option:
+        --with-bug-report-url=https://example.com/
+      so that you can filter packaging bugs from core bugs before
+      reporting upstream.
+"
+fi
 
 ######################################
 # Checks for gtk-doc and docbook-tools
@@ -2829,7 +2857,9 @@ Tests:
   Use xvfb-run             $have_xvfb_run
   Test appdata             $have_appstream_util
   Test desktop file        $have_desktop_file_validate
-$have_recommended_xgettext$have_recommended_gtk$warning_vector_icons_windows$warning_glib_networking$warning_gcc"
+
+Bug report URL: $with_bug_report_url
+$override_bug_report_url$have_recommended_xgettext$have_recommended_gtk$warning_vector_icons_windows$warning_glib_networking$warning_gcc"
 
 if test "x$required_deps" = "x"; then
   AC_OUTPUT