please avoid tabs

[Werner LEMBERG]

Folks,


something that can be easily missed while doing reviews with Rietveld:
Since a long time we avoid tabs if possible.


    Werner


PS: I've cleaned up `configure.ac` and `aclocal.m4` in the staging
    branch.

PPS: I see that we have a file `.dir-locals.el` in the git repository;
     doesn't its contents contradict our tabs policy?  The texinfo
     column length of 66 chars only seems also too low (should be 78
     IMHO).