Fix lua bindings for timestamp precision

The changes to the timestamp define names broke the init.lua file
generation.  Change-id Id0c27b31c5 tried to fix this, but would break
backwards compatibility of exisitng Lua scripts.  This commit fixes
that change by adding the timestamp variables in both a new Lua table
as well as the old filetypes table.

Change-Id: I74749acb51dc85094e8c63b240a1951bd4cc0330
Reviewed-on: https://code.wireshark.org/review/4370
Reviewed-by: Evan Huus <eapache@gmail.com>