camera.* attribute proposal

[Artem Kachitchkine]

> Currently there is a camera.access_method which, afaict, can currently 
> hold at least 2 values: 'ptp' and 'libgphoto2' where 'libgphoto2' 
> incldues at least usb mass storage cameras and some proprietary protocols.

According to the spec:

http://cvs.freedesktop.org/*checkout*/hal/hal/doc/spec/hal-spec.html?only_with_tag=HEAD#device-properties-camera

camera.access_method can be either 'storage' or 'user'.
And there's the camera.libgphoto2.support boolean property that says 
whether the device is supported by libgphoto2.

0.5.4 also includes fdi/information/10freedesktop/10-camera-ptp.fdi, 
which sets access_method to 'ptp' for USB interfaces:

     <match key="info.bus" string="usb">
       <match key="usb.interface.class" int="0x06">
         <match key="usb.interface.subclass" int="0x01">
           <match key="usb.interface.protocol" int="0x01">
             <merge key="info.category" type="string">camera</merge>
             <append key="info.capabilities" type="strlist">camera</append>
             <merge key="camera.access_method" type="string">ptp</merge>

Kinda like what you've just proposed.

-Artem.