Add-on for debhelper to call autoreconf and clean up after the build

dh-autoreconf provides a debhelper sequence addon named 'autoreconf' and
two commands, dh_autoreconf and dh_autoreconf_clean.

The dh_autoreconf command creates a list of the files and their checksums,
calls autoreconf and then creates a second list for the new files.
 
The dh_autoreconf_clean command compares these two lists and removes all
files which have been added or changed (files may be excluded if needed).

For CDBS users, a rule is provided to call the dh-autoreconf programs at
the right time.