evolved from issue 23349

scenario :
create new spreadsheet
format cell a1 as number, a2 as text
select row a by clicking on label
format it as number
cell a2 hasn't type changed.

as explained, this is an intended behaviour, but this results in a problem, when 
a user wants to change all cells to some specific type.

so, a suggested action :
if, for some reason, selected range contains different cell types and some of 
them would not be changed in a default behaviour, display a dialog that explains 
this situation (it maybe even has a button {details} that further describes 
cells that have questionable type and what would happen with these cells) and 
asks the user if [s]he wants to force changing of cell type for all cells or 
change it only for those cells that oo.org suggests. it also could have a 
checkbox/option that would set one of these behaviours as default so that this 
dialog doesn't show up again. this option should be easily changeable 
thereafter, of course.

although it is nice that oo.org tries to save user from mistakes, current 
behaviour is quite irritating : changes are dropped silently and there is no way 
for user to clearly see what and why didn't happen the way [s] he wanted. also, 
there is no way to change cell type for all cells (except changing it to some 
other, third type, and then to final type - but that's not exctly the easiest 
way).