reversal of brace vs process expansion needs compatibility option

[Ted Bagg]

Dear Bash maintainers, this very useful construct worked in 3.2:

diff  <(sort {a,b}.lst)

but fails in 4.0, breaking scripts for many, no doubt.  Such a 
substantive change (much more harm than good, in my opinion) ought 
always to come with an option to revert to the previous behavior.

Sincerely,
Ted Bagg