Bugfix/osx set dynamiclib

Currently OSX cannot find the dynamic library if it is installed in a non-system directory without setting environment variables:
```
dyld: Library not loaded: libzlog.1.2.dylib
  Referenced from: /Users/basho/dev/clients/c/riak-c-client/./build/riak_c_client
  Reason: image not found
Trace/BPT trap: 5
```
 This change encodes the target path but requires the PREFIX to be set at build time since it is encoded in the dylib  as mentioned in the GettingStarted-X.txt files.