[tlbuild] How to properly regenerate configure files?

[Karl Berry]

    gregorio/configure.ac and gregorio/gregorio-src/configure.ac differ 

There is no simple answer.

Some stuff is implied by KPSE_COMMON or other TL automacros, or
otherwise unnecessary in TL (check for kpathsea).

Some stuff -- e.g., the maximal pedanticism -- is undesirable for TL.
In general, for "simplicity", Peter and I did not want to pull in AX_*
macros unless it was actually necessary, and it did/does not seem to be so.

And, some stuff may have been missed.  I don't know, I'd have to study
every individual line.  -k