ALLJOYN-1676 scons incorrectly assumed daemon_libs[1] was a *.lib file

The scripts used the fact that the libraries were always in the same location
when in the daemon_libs variable. With the change in build_core for ALLJOYN-1676
this was no longer always true. So we must search the daemon_libs variable list
to find the scons.file.nodes that contain the shared and static daemonlib libraries.
ALLJOYN-1769 Do not enable read callbacks until the message is unmarshalled.

Change-Id: I0414b713c3fe98228d63e89fb08aaa27c343af76
ALLJOYN-1767 Fix invalid iterator in ExchangeNamesSignalHandler.

Change-Id: I1d2c8c70577925ffb955fac0c351be7574ba658d