[bug report] autoheader still creates .in file if no AC_CONFIG_HEADERS

[Kelley Cook]

If you run autoheader 2.59b on a configure.ac without a 
AC_CONFIG_HEADERS, it will properly inform you

error: AC_CONFIG_HEADERS not found in configure.ac

Nevertheless the perl script continues which appends .in to nothing 
thereby creating the hidden file ".in" and procedes all outputs all the 
defines into it.

Two easy solutions would be to either abort after the error or to set a 
default for $config.h |= "config.h" right after the error message.

There are likely other solutions to this bug.

Kelley Cook