postgresql: new package

Based on suggested new package by Marco Trapanese ([1]).

[1] http://lists.busybox.net/pipermail/buildroot/2014-February/090661.html



[Thomas: make it only available with glibc toolchains.]

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>