[patches against bzr master attached (hopefully!)]

hi,

i believe this is a bug in comint-read-input-ring. shell-mode sets a  
buffer-local version of comint-read-input-size which is effectively  
ignored due to comint-read-input-ring's use of '(with-temp-buffer ...'  
. i've lost ~40000 line bash history on more than one occasion over  
the last several years and am elated to have finally pinned the  
problem on something

(very loosely) related to this issue is the question of why the  
default of 'comint-input-history-ignore' is set to anything at all?  
it's currently "^#", and therefore without having pro-actively made  
any changes to their emacs setup, a user's shell history (for  
instance) doesn't emerge unscathed from a trip through comint if it  
contains comments. if modifying this default touches too many other  
comint uses, perhaps an override in shell-mode.el?

cheers,
Pete