only hit up dlsym once per function instead of once per call
only hit up dlsym once per function instead of once per call

git-svn-id: 2ee24f9a0920b584ad60d19d1988b34a1f0c00a6@6 0b19fab4-3b79-e111-ab8d-001cc008e099

plausiblelabs/PLWeakCompatibility