Error when nest.helpdesk() is called with Python < 2.7.8

[janhahne]

When I install NEST with Python 2.7.6 and then call nest.helpdesk() in python I get an error that the file helpindex.html does not exist. If I call nest.help('iaf_psc_alpha') (or any other NEST object) i get the - of course somehow right - answer Sorry, there is no help for 'iaf_psc_alpha'!

I assume this behavior results from the combination of PR #688 and #715.

When I call nest.helpdesk() or nest.help(object) with Python 2.7.6 I would expect an information as The NEST help is not available due to a Python version older than 2.7.8. Otherwise it is unclear to the user what is going wrong - there is no message at all, neither when the help is accessed via python nor while cmake (which might be useful as well?)

[heplesser]

@steffengraber Could you take a look at this? I think @janhahne's suggestion to print

NEST Help is not available on Python 2.7.7 and earlier.

[steffengraber]

@janhahne @heplesser There is a little fix: #751.
Please test and review it.