user_ident_sufficiently_given(): refactor the logic to be usable from elsewhere

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/ident.c b/ident.c
index d4f6145..96b56e6 100644
--- a/ident.c
+++ b/ident.c
@@ -259,3 +259,12 @@
 			 getenv("GIT_COMMITTER_DATE"),
 			 flag);
 }
+
+int user_ident_sufficiently_given(void)
+{
+#ifndef WINDOWS
+	return (user_ident_explicitly_given & IDENT_MAIL_GIVEN);
+#else
+	return (user_ident_explicitly_given == IDENT_ALL_GIVEN);
+#endif
+}