Hello,

Thanks for all comments (on and off list).
Attached an updated patch with documentation.

The supported options are:

  --default-signal[=SIG]  reset signal SIG to its default signal handler.
                          without SIG, all known signals are included.
                          multiple signals can be comma-separated.
  --ignore-signal[=SIG]   set signal SIG to be IGNORED.
                          without SIG, all known signals are included.
                          multiple signals can be comma-separated.
  -p                      same as --default-signal=PIPE

(lower-case "-p" as to not conflict with BSD, but of course can be
changed to another letter).

The new 'env-signal-handler.sh' test passes on GNU/linux, non-gnu/linux
(alpine), and Free/Open/Net BSD.

Comments very welcomed,
  - assaf