debian patches to exit with code 127 for nonexistent/directory scripts

[Jilles Tjoelker <jilles@stack.nl>]

Debian's dash package has some local changes which cause an exit with
code 127, as required by POSIX, if a script (passed with dash
<filename>) cannot be opened or cannot be read because it is a
directory.

Unfortunately, these patches also affect the . builtin (if the pathname
contains a slash) and use EXEXIT, which means such errors always cause
the shell to exit, even in interactive mode or if the builtin's
specialness has been disabled using command.

% dash
$ . ./nonexistent
.: 1: Can't open ./nonexistent
zsh: exit 127   dash
%

% dash -c 'command . ./nonexistent; echo continued'

Note: Do not compare this with bash. Bash deliberately does not follow
POSIX XCU 2.8.1 Consequences of Shell Errors if not in POSIX mode, and
even in POSIX mode trying to source a nonexistent dot script (without
slash in the pathname) fails to abort the shell.

Note 2: POSIX seems unclear about what 'command .' should do, but is
very clear that failure to find/read a dot script shall not cause an
interactive shell to exit.

-- 
Jilles Tjoelker