autotools update

[Hans-Bernhard B. <HBB...@t-...>]

Hello all,

I went ahead and committed the auto tools update mentioned in two 
earlier discussions.  The only major difference you're likely to notice 
is that configure.in has been renamed configure.ac.  CVS doesn't really 
support file renames, so this had to be done by adding the new and 
dropping the old.

The other noticable effect is that the test for RETSIGTYPE was removed, 
so its value is now fixed to its former default value of 'void' from 
syscfg.h.  We could s/RETSIGTYPE/void/g later, but for now, the existing 
definition works as well.

HBB