m4_text_box => AS_TEXT_BOX?

[Paolo Bonzini]

m4_text_box is the sole user of quadrigraphs in m4sugar.m4.  Together
with m4_warn, in turn, it is the sole feature needing autom4te.  I don't
care about m4_warn very much, but it would be nice to rename m4_text_box
to AS_TEXT_BOX and move it to m4sh.

Bison does not use it, and Google says it is unused:

http://google.com/codesearch?hl=en&sa=N&filter=0&q=+-file:(autoconf|autotest|m4sh|m4sugar).m4(f|)+-package:autoconf+m4_text_box

but after all it is documented.  How much does this make it a deal-breaker?

Paolo