Add /lib64/pkgconfig in PKG_CONFIG_PATH to support centos6.6

Change-Id: I7af048213211a257482134753ad765e127f9d4b1
Remote API reviewed.

We now provide a new set of API with a uniform style.
The main benefit is now to handle session ID's in all RPC.
These session identifiers are already handled by the redcurrant daemons, and propagating a single session id in all the requests belonging to a single session really helps to consolidate the logs.

Change-Id: Iec8969fed2f1280822d92d1575ccf7e15b46cd42