Description of problem:
The zsh command_not_found_handler has slighty different semantics, which make it less useful:
1 If the handler returns non-zero, the shell itself returns 127, regardless.
2 If the handler returns non-zero, the shell always prints an error message 'command not found', regardless.

This makes it impossible to differentiate an error with the handler (say, a user chose not to install the program with PackageKit), or an error code from the program. Also, this may print a command not found error, when the command actually launched.

In bash, this would be 0 if the handler installed the program, and it ran successfully, 127 if the handler didn't exist, or had an error, anything else, if the program exited with this error code.


Version-Release number of selected component (if applicable):
zsh-5.0.2

How reproducible:
100%


Steps to Reproduce / Actual results:
[user@host ~] $ zsh
[user@host] ~% not-found
zsh: command not found: not-found
[user@host] ~% echo $?
127
[user@host] ~% function command_not_found_handler() { return 0; }
[user@host] ~% not-found
[user@host] ~% echo $?
0
[user@host] ~% function command_not_found_handler() { return 3; }
[user@host] ~% not-found                                         
zsh: command not found: not-found
[user@host] ~% echo $?                                           
127
[user@host] ~% function command_not_found_handler() {
  echo "Command not found" >&2; return 127; }
[user@host] ~% not-found                                                                         
Command not found
zsh: command not found: not-found
[user@host] ~% echo $?                                                                           
127

Expected results:
[user@host ~] $ zsh
[user@host] ~% function command_not_found_handler() { return 0; }
[user@host] ~% not-found
[user@host] ~% echo $?
0
[user@host] ~% function command_not_found_handler() { return 3; }
[user@host] ~% not-found                                         
[user@host] ~% echo $?                                           
3
[user@host] ~% function command_not_found_handler() {
  echo "Command not found" >&2; return 127;
}
[user@host] ~% not-found                                                                       Command not found
[user@host] ~% echo $?                                                                           
127


Additional info:
For bash:

[user@host ~] $ unset command_not_found_handle
[user@host ~] $ not-found
bash: not-found: command not found
[user@host ~] $ echo $?
127
[user@host ~] $ function command_not_found_handle() { return 3; }
[user@host ~] $ not-found
[user@host ~] $ echo $?
3
[user@host ~] $ function command_not_found_handle() {
  echo "Command not found" >&2; return 127;
}
[user@host ~] $ not-found
Command not found
[user@host ~] $ echo $?
127