List devices + static to track if sdk intialised

[elliotwoods]

Heya

I dont expect you to pull this, but perhaps with some style changes it could be suitable.

Basically 2 main things are:

1. listDevices outputs either to console or to a string (or this could be a vector of info's for more developer level access, perhaps a seperate function "listDevices(vector &l)" which is called by existing listDevices.
2. Track whether sdk is already intialised in a static bool - necessary (afaik) for > 1 camera to be operational. The current nature of terminate/initialise probably needs a little more attention. (especially when releasing).

Noted that before and after these changes, cameras do no shut down correctly on close.

Tested on OSX 10.7, 550D + 5D Mk2.

[elliotwoods]

in the listDevices commit i appear to have included changes to example code
that's an accident. but as i said i'm not expecting a pull so will fix later when listDevices / statics are more decided

[kylemcdonald]

just wanted to say thanks -- i'm going to leave this in the PRs because it has some weird stylistic things and i can't personally test it myself, but it may be useful to someone else.