Fix 64-bit VS2013 build

Do not pull in libethereum/Client.h into QT.
This is not necessary the most sane thing to do, but without it I cannot avoid getting 
C:/Program Files (x86)/Windows Kits/8.1/Include/um/winsock2.h(949): error : Can't concatenate non identifier tokens
erros.
Merge pull request #294 from SharpCoiner/patch-2

Fix 64-bit VS2013 build