Partially fix a few issues wiht fidlib

This was breaking for me when externalizing fidlib.  Other places in the src currently use #include 
&lt;fidlib.h&gt;.

The fidlib api has been patched int he mixxx source which is causing some issues for external depends.  Has upstream been notified of these "fixes?"  Is this project still developed?  If not, time for a fork?  This patch includes a ~~workaround~~ hack for the api breakage that just copies the const string to a dynamic one to satisfy the api.