libperconaserverclient for PS5.1

For our packages to be included in Linux distributions we must not conflict with existing packages of Oracle MySQL. At the most basic level this means our client library packages cannot be named "libmysqlclient". The next level of this is to not install libmysqlclient.so that conflicts with the Oracle packages, as this runs the risk of ABI incompatibility that would just be annoying for all involved.

Proposal is to have libperconaserverclient.so, in libperconaserver packages and if you install the libperconaserver-dev package, then the mysql_config binary installed will point to PS client libs, if you install the Oracle one then you get Oracle libs.