Intermediate fix for min_wd in tables

In tables, calculating min_width was broken as it only stops
at glue nodes. It must take the real hyphenation patterns into
account. Now that we have allowbreak="xyz" the text might
not even break at the glue node.

This fix is not final, as I have to find out why there are
minor overfull hbox messages (0.5pt too wide and such)