5100_H_INCLUDED is defined in w5100.h but that file is not included from
I didn't notice it was on ethernet1.. it is not on 2... it is only use by socket I think... good point
I'm not sure why you're including the last two
when you do an automatic include via windows menu of ethernet library, it does include it. I ask myself eater if it is needed... 
You could resolve that by moving the code from testlib.cpp to testlib.h
did you more think of moving the code from ino to header ?
I think this is what I will do.
[EDIT] the bug of compiler that see multiple def of dhcp and dns and blabla... that was in fact cause by my inclusion of dhcp and dsn on sketch !! good point. remove it make thing easier.