There seems to be overlap in the implementations and usage of
gnus-buffer-exists-p and gnus-buffer-live-p, as well as of gnus-buffers
and gnus-prune-buffers.

The attached patch removes gnus-buffer-exists-p in favour of a modified
gnus-buffer-live-p, aliases gnus-prune-buffers to a simplified
gnus-buffers, and simplifies several call sites pertaining to buffer
liveness checking and killing.  WDYT?

Thanks,

-- 
Basil