* doc/automake.texi (Texinfo): Define MAKEINFO, MAKEINFOHTML,

* doc/automake.texi (Texinfo): Define MAKEINFO, MAKEINFOHTML,
MAKEINFOFLAGS, AM_MAKEINFOFLAGS, AM_MAKEINFOHTMLFLAGS, TEXI2DVI,
TEXI2PDF, DVIPS, and TEXINFO_TEX in a table.
(Uniform): Do not speak of missing HTML support, this is
confusing.
* lib/Automake/Variable.pm (_silent_variable_override): Add
AM_MAKEINFOHTMLFLAGS.
* lib/am/texibuild.am (%SOURCE_SUFFIX%.html): Use MAKEINFOHTML and
AM_MAKEINFOHTMLFLAGS instead of MAKEINFO and AM_MAKEINFOFLAGS.
* lib/am/texinfos.am (MAKEINFOHTML, AM_MAKEINFOHTMLFLAGS): Define.
* tests/txinfo21.test: Add a test with AM_MAKEINFOHTMLFLAGS.