Fix OS X 10.10 compatibility issue

In current version of OS X 10.10 Yosemite beta, Apple took the name `htonll` for their new macro, zookeeper ruby client fails to build.
To fix this issue, I replaced every occurence of `htonll` by `zk_htonll` from the sources and header files in `zkc-3.4.5.tar.gz`. More specifically, these files were changed to fix this issue:

* c/include/recordio.h
* c/src/recordio.c
* c/src/zookeeper.c
* c/tests/ZKMocks.cc

Hope this little modification helps others who are using OS X 10.10 beta.