Fix white space in config/configure.ac_scripts/*.dir_list
In autogen.sh improve comments/output
In autogen.sh automatically handle new builds

Set generate_config_files flag by default if this is a new build, i.e.
if ./configure does not exist.

This means everything normally done by --rebuild will run by default for
new builds.
Move automake compatability hack into autogen.sh
Remove regenerate_config hacks from build machinery

Now running autogen.sh should automatically select the required build
steps in every case! Everything should just work and you should never
need to run it with the --rebuild option.

This will also massively speed up rerunning autogen in many cases
because ./configure is only run if it is really needed (previously it
was always run).

We are now almost using autotools in the "approved" way,
except that we generate the list of user directories automatically and
allow specification of configure options from a file.

The changes needed were:

* Include the directory list file into configure.ac properly.

* Use `autoreconf -i` instead of attempting (and failing) to run the
  right selection of autotools commands manually. This allows make to
  automatically detect when the driver list file has changed and rerun
  the necessary commands.

* Add code to autogen.sh to detect when the configure options have
  changed and force the rerunning of autoreconf automatically (instead
  of needing to specify a rebuild).

* Remove regenerate_config_files.sh and related files because they are
  no longer needed.
In autogen.sh fix bug with -h if run from another directory
In interactive_autogen.sh check we are in the correct dir
In autogen.sh clarify some comments
In autogen.sh combine all "first build" stuff

There are a number of things that need to run if this is the first time
we have built oomph-lib here (or if a rebuild has been forced). Move
them all into one section of the code.