#775964: skip YP/NIS entries instead of failing the test

Also includes doc updates mentioning that these entries may not
be retrievable via getgrnam and getgrgid.

Patch by Bobby Impollonia.
diff --git a/Misc/ACKS b/Misc/ACKS
index bc5821d..5dfb8da 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -398,6 +398,7 @@
 Fredrik Håård
 Mihai Ibanescu
 Lars Immisch
+Bobby Impollonia
 Meador Inge
 Tony Ingraldi
 John Interrante