- Changed the representation of colElem to support a few cases
  for some languages not supported by the current format.
- Changed offsets for implicit primary values. This makes the
  values both easier to read and debug (last 4 nibbles are identical to
  implicit primary value) and also results in better packing.
- Fixed bug in weight conversion code that did not pop up yet by
  sheer luck.
Note that tables.go also includes changes to the contraction trie
from CL 6346092.

R=r, mpvl
CC=golang-dev
https://golang.org/cl/6392060