DM-1661: czar log4cxx link/load bug on Ubuntu 14.04

On Ubuntu 14.04, the czar would fall over at load time with an unresolved
sym (for typeinfo for log4cxx::helpers::ObjectPtrBase) while loading the
css python wrapper shared lib. It seems the linker was tripping up chasing
transitive dependencies through the shared libs.

This cl tweaks core/modules/Sconscript to provide additional explicit link libs
to "shmod" shared modules to hint the linker.
Merge branch 'u/fritzm/DM-1661'