Separate table functions that format their arguments from those that don't.

The tab_text, tab_joint_text, and tab_output_text functions, until now,
had an option bit TAT_PRINTF that specified whether they passed their text
argument through sprintf.  This interface was bad because it made it
impossible for GCC to tell whether it needed to verify a printf format
string or not.

This commit solves the problem by breaking each of these functions into one
that does format its argument and one that doesn't.