dahdi_genconf: Add 'modules', 'spantypes', and 'assignedspans' to list of available generators.

This is a documentation change, that hopefully will help until I can remember
the names of the new generators.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
dahdi_span_types: Show location of configuration file in help message.

Makes similar in for the dahdi_span_assignments in that the location of the
default configuration file is shown in the help screen.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
dahdi_cfg: Add semaphore to prevent parallel execution.

When dahdi is configured for fully dynamic configuration on a device and
span basis via sysfs and udev it is possible for multiple instances of
dahdi_cfg to be run in parallel on different spans. If this happens it
is possible to see errors on the console that tone zones are already
registered since the check for the existence of a tone zone and the
re-registering needs to be atomic.

dahdi_cfg will now prevent itself from running in parallel.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
dahdi_handle_device, dahdi_span_config: Check for auto_assign_spans only when ACTION is add.

When dahdi.ko is unloaded, it may be possible for the driver to be removed from
the kernel before the udev scripts are run.  When this happens, you'll see
messages like the following which are not accurate:

    'dahdi_handle_device'[24567]: Old driver (no auto_assign_spans parameter). Skip /devices/pci0000:00/0000:00:1e.0/0000:11:01.0/pci:0000:11:01.0

Now instead you will see:

    'dahdi_handle_device'[28008]: remove: /devices/pci0000:00/0000:00:1e.0/0000:11:01.0/pci:0000:11:01.0

Also, all the udev events will be logged in the system log even when they are
ignored because of legacy auto span assignment. This will help show what is
going on during the transition period to full udev configuration of spans.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
Acked-by: Oron Peled <oron.peled@xorcom.com>