Build with automake-1.13 broken

Automake-1.13 removed long obsolete AM_CONFIG_HEADER completely ( http://lists.gnu.org/archive/html/automake/2012-12/msg00038.html ) and errors out upon seeing it.

Attached patch replaces it with proper AC_CONFIG_HEADERS.

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I'm mass-submitting automake-1.13 fixes. Please see what you can do so I don't need to do the same when automake-1.14 comes out: http://cazfi.livejournal.com/195108.html