Switch to storing string form of error quarks

Instead of storing the name of the function to call to get the
error quark, store the string form of the error quark, which
we derive from the introspection binary during scanning.

Update EnumBlob and GIEnumInfo to include the new information.

This will allow determining a back-mapping from error quark
to error domain without having to dlsym() and call all the
known error quark functions.

Based on earlier patches from Owen Taylor and Maxim Ermilov.

https://bugzilla.gnome.org/show_bug.cgi?id=602516

gitypelib-internal.h

@@ -798,6 +798,8 @@ typedef struct {
  * (will be a signed or unsigned integral type)
  * @gtype_name: String name of the associated #GType
  * @gtype_init: String naming the symbol which gets the runtime #GType
+ * @error_domain: String naming the #GError domain this enum is
+ *   associated with
  * @n_values: The lengths of the values arrays.
  * @values: Describes the enum values.
  */
@@ -817,7 +819,7 @@ typedef struct {
   guint16   n_values;
   guint16   reserved2;
 
-  guint32   reserved3;
+  guint32   error_domain;
 
   ValueBlob values[];
 } EnumBlob;