Autoconf upgrade

- Set the version number to 2.6.0
- Upgrade to autoconf 2.68
- Set the bug report address to the liblouis list
- Set the package url to the new web site


git-svn-id: http://liblouis.googlecode.com/svn/trunk@1167 24698d54-e344-0410-af24-25bd253c2c7b