Error: Introduce error_copy()

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
diff --git a/error.h b/error.h
index 6361f40..45ff6c1 100644
--- a/error.h
+++ b/error.h
@@ -35,6 +35,11 @@
 bool error_is_set(Error **err);
 
 /**
+ * Returns an exact copy of the error passed as an argument.
+ */
+Error *error_copy(const Error *err);
+
+/**
  * Get a human readable representation of an error object.
  */
 const char *error_get_pretty(Error *err);