I found the file, tabl-tbl.mkiv, here:
/usr/local/texlive/2013/texmf-dist/tex/context/base/tabl-tbl.mkiv
I insert the line you said that was missing at line #721.
But, it did not change anything. Does this file need to be compiled or anything?
I am not familiar with the deeper workings of ConTeXt code yet.
You have generate a new format file where all source files are stored in a single file.
When you type "context --touch --expert" on the command lines context
generates a new format file when you process your document the next time.
Wolfgang