QPID-4704: Build legacystore.so as a module, not a shared library.

Fixes the legacystore.cmake file to build the file appropriately, and
als includes a directive to install the module along with others.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1465015 13f79535-47bb-0310-9956-ffa450edef68