+ First try to detect the OS X native dynamic linker before falling
      back to dlfcn.h.
    + Enhanced the dlopen-style loader detection.
    + Added a check for HP-UX's shl_* functins.
  * src/misc/modules_plugin.h.in:
    + Support for the dylib dynamic loader on OS X.
    + Support for the shl dynamic loader on HP-UX.