Add intra-version 1.5.1 mappings for MCP update in Forge 646 -> 647

These mappings are from the old version of MCP csvnames (in Forge 7.7.1.646)
to the recently released update (in Forge 7.7.1.647+). Intended for helping
modders (with Forge mods written using pkgmcp names) update to the new names.

Created by chaining old and new MCP mappings:

/tmp/new.srg: https://raw.github.com/agaricusb/MinecraftRemapping/46f121acfd45b850ee760d1afa3aedc405df754a/1.5.1/pkgmcp2obf.srg
/tmp/old.srg: https://raw.github.com/agaricusb/MinecraftRemapping/fc939826a4edd44bf151770a961ab50c2fb66d2a/1.5.1/pkgmcp2obf.srg
py chain.py ^/tmp/new.srg ^/tmp/old.srg|python rmdupes-srg.py > 1.5.1/updatemcp-646-to-647.srg

For update:

MinecraftForge/FML@1774e2bf3073c3449d1f289399971ad93a5b6479
MinecraftForge/MinecraftForge@7c6468a9ea956e743e2e8c7314808525a65e6ebc