hyphen/minus fixes in man pages

in groff '-' creates a hyphen and for a minus (path, option, or similar)
you need '\-'.

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
hotplug: document asterisk scriptlet

A well-behaving distribution may choose not to install
span_config.d/50-asterisk as part of dahdi-tools, as it belongs in
asterisk. Still, it would be nice to be able to keep it as a documented
usage example. So just writ where this file needs to go and what it
does.

No other change: it is still installed by default.

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
README: udev hooks run scripts from directories

Signed-off-by: Tzafrir Cohen <tzafrir.cohen@xorcom.com>
hotplug: Do not run auto span configuration if spans are auto assigned.

This reapplies the change made in commit (6ed0adc08 "dahdi_span_config: Do not run auto
span configuration if spans are auto assigned.") which appears to have been
accidentally removed in (7f826a7d35 "hotplug modularization: split logic to
scriptlets").

To rationale from commit 6ed0adc08:

I have seen cases were users run:

  # modprobe <driver>; dahdi_cfg -c <custom config file>

and the spans end up misconfigured because dahdi_span_assignments ends up
running, via udev, after the user configured the span the way it wanted.

dahdi_span_assignments now looks at auto_assign_spans module parameter on
dahdi.ko, like dahdi_handle_device already does, to determine if legacy or udev
based configuration is being done.

Signed-off-by: Shaun Ruffell <sruffell@digium.com>