doc, vtysh: Fixup of history handling

This fix does two things:

1) If the ${HOME}/.history_quagga file does not exist, create it
for history storing.
2) Allow vtysh -c "..." commands to be stored in history file
as well

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>
diff --git a/vtysh/vtysh_user.h b/vtysh/vtysh_user.h
index c485c23..a6c8b99 100644
--- a/vtysh/vtysh_user.h
+++ b/vtysh/vtysh_user.h
@@ -25,4 +25,6 @@
 int vtysh_auth (void);
 void vtysh_user_init (void);
 
+char *vtysh_get_home (void);
+
 #endif /* _VTYSH_USER_H */