cap_app/util: add debug option and printouts for debugging dropped frames.

note that currently everthing seems to be 'as expected', but that
doesn't mean it's good: in the worst case, if proc updates are at the
same rate as the frame updates, long sequences of captured frames can
be dropped/non-displayed, even though all frames are read from the
camera *and* the GUI/display is never stuck. neat! anyway, N-way
buffer sharing should make the curent in_redisplay handling go away so
then it would be moot. otherwise we could probably fix/change things
to give a better result.
boda_base/cap_app: mostly-fix duplication between ASIO and iostreams flavors of bread/bwrite.

it's not the prettiest thing. ah, c++ template. maybe we can do better later ...
boda_base: add generic {bread,bwrite}_bytes() support/declarations for
all classes with a nested has_bread_bwrite typedef
cap_app: add multi read/write support, use it to share p_img_t across all 3 processes in cs_disp.

add various comments on the limitations/properties of the current setup. as a semi-side-effect, the display shouldn't 'drop' captured frames anymore, since we don't sometimes ignore them on purpose anymore. note that the display *only* updates on new captured frames now, which isn't quite ideal/right ...
cap_app/cs_disp: share capture image with proc process too.

remove now-unneeded proc_in_img from capture process. proc process does copy to output buffer now (which is the only copy needed). tweak proc process comm to read directly to proc_done var.