Growl notifications: Fix attempts to pass std::string instead of const char*

This is required on OS X due to the recent return type changes for the
gettext functions.
Xcode project: switch to using the new boost filesystem code

This includes adding a new library (libboost_localew.dylib; with
libboost_filesystemw.dylib already having been added a few days ago),
so a new version of the Mac compile package is needed for compiling.