Clean up handling of `gen` exits in `gen_statem`
Clean up handling of `gen` exits in `gen_statem`

The `gen` module raises `exit` exceptions when it
detects an error.  Clean up handling of these by
not handling other classes of errors, to not
accidentally bury an interesting cannot-happen-error.

rlipscombe/otp,mikpe/otp,jj1bdx/otp,dgud/otp,dumbbell/otp,jj1bdx/otp,isvilen/otp,mikpe/otp,vinoski/otp,emacsmirror/erlang,dgud/otp,erlang/otp,potatosalad/otp,potatosalad/otp,isvilen/otp,isvilen/otp,mikpe/otp,vinoski/otp,dumbbell/otp,erlang/otp,dumbbell/otp,erlang/otp,dumbbell/otp,emacsmirror/erlang,emacsmirror/erlang,jj1bdx/otp,g-andrade/otp,vinoski/otp,mikpe/otp,mikpe/otp,isvilen/otp,g-andrade/otp,g-andrade/otp,isvilen/otp,bjorng/otp,g-andrade/otp,rlipscombe/otp,dgud/otp,mikpe/otp,bjorng/otp,erlang/otp,dumbbell/otp,bjorng/otp,dgud/otp,vinoski/otp,potatosalad/otp,bjorng/otp,g-andrade/otp,g-andrade/otp,isvilen/otp,erlang/otp,potatosalad/otp,mikpe/otp,emacsmirror/erlang,rlipscombe/otp,dgud/otp,rlipscombe/otp,jj1bdx/otp,emacsmirror/erlang,dumbbell/otp,bjorng/otp,bjorng/otp,g-andrade/otp,isvilen/otp,rlipscombe/otp,dumbbell/otp,erlang/otp,mikpe/otp,vinoski/otp,jj1bdx/otp,rlipscombe/otp,potatosalad/otp,potatosalad/otp,erlang/otp,emacsmirror/erlang,g-andrade/otp,bjorng/otp,jj1bdx/otp,dumbbell/otp,jj1bdx/otp,dgud/otp,vinoski/otp,erlang/otp,rlipscombe/otp,emacsmirror/erlang,rlipscombe/otp,emacsmirror/erlang,emacsmirror/erlang,jj1bdx/otp,vinoski/otp,potatosalad/otp,vinoski/otp,dgud/otp,g-andrade/otp,potatosalad/otp,dumbbell/otp,rlipscombe/otp,emacsmirror/erlang,isvilen/otp,dgud/otp,jj1bdx/otp,vinoski/otp,g-andrade/otp,dgud/otp,bjorng/otp,mikpe/otp,potatosalad/otp,dumbbell/otp,dgud/otp,vinoski/otp,mikpe/otp,potatosalad/otp,bjorng/otp,isvilen/otp,isvilen/otp,erlang/otp,erlang/otp,jj1bdx/otp,bjorng/otp,rlipscombe/otp