This patch modifies the zonetabconversion.py script to look also in the /usr/share/libtimezonemap/backward file for old timezones that have been renamed over the years. For example Asia/Calcutta is now known as Asia/Kolkata
this is useful because sometimes you encounter the older names in calendar incidence.
technically the patch is only the zonetabconversion.py script, but I included the new tztable.h it generates so you can see what the changes will be.