NOTPARALLEL rule for documentation directory

[John W. Eaton]

On 28-Aug-2012, Rik wrote:

| I noticed in the discussion of octave.html no longer building that the
| .NOTPARALLEL directive was commented out in the same changeset
| (http://hg.savannah.gnu.org/hgweb/octave/rev/017f0b2e6933).  Has something
| changed in Automake to make this directory parallel-safe?  Otherwise, I
| think it is still needed.  As the comment says, it isn't our Makefile rules
| that are failing, but the auto-generated ones which we don't have control of.

I haven't noticed problems due to parallel make since commenting it
out.  Do you remember specifically what were the problems?

jwe