libx11-6-dbg 6.8.2-10.4 (i386 binary) in ubuntu hoary

 This package is useful to provide a backtrace with symbol names in a
 debugger; this facilitates interpretation of core dumps, and aids in finding
 logic errors in programs using this library (or the library itself). The
 library is installed in /usr/X11R6/lib/debug and can be used by placing that
 directory in the LD_LIBRARY_PATH environment variable when the code to
 be debugged is executed.
 .
 Unstripped versions of Xlib's loadable modules for internationalization
 support are provided in /usr/X11R6/lib/debug/X11/locale/lib/common. Note
 that if you wish to debug these modules, you will need to set XLOCALEDIR to
 /usr/X11R6/lib/debug/X11/locale. Also note that for security reasons,
 unprivileged users are unable to override XLOCALEDIR in this way, so you may
 have to perform your debugging of the Xlib modules as root.
 .
 Non-programmers will likely have little use for this package. See the
 libx11-6 package for further information.