scripts/sphinx-pre-install: add how to exit virtualenv usage message

# Common dependencies

#

sub deactivate_help()

{

	printf "\tIf you want to exit the virtualenv, you can use:\n";

	printf "\tdeactivate\n";

}

sub check_needs()

{

	# Check for needed programs/tools

		if ($need_sphinx && scalar @activates > 0 && $activates[0] ge $min_activate) {

			printf "\nNeed to activate a compatible Sphinx version on virtualenv with:\n";

			printf "\t. $activates[0]\n";

			deactivate_help();

			exit (1);

		} else {

			my $rec_activate = "$virtenv_dir/bin/activate";

			printf "\t$virtualenv $virtenv_dir\n";

			printf "\t. $rec_activate\n";

			printf "\tpip install -r $requirement_file\n";

			deactivate_help();

			$need++ if (!$rec_sphinx_upgrade);

		}