shell's 'errexit' option and variable definition.

Shell's option 'errexit' works unexpectedly when command returning non-zero
is called in `local` variable definition statement.

Let's see on example:

    f2()
    {
        echo -n "f2(): " >/dev/stderr
        set -o | grep errexit >/dev/stderr
        echo "subsh=$BASH_SUBSHELL" >/dev/stderr
        echo 'Failed' >/dev/stderr
        return 1
    }

    f1()
    {
        echo -n "f1(): " >/dev/stderr
        set -o | grep errexit >/dev/stderr
        echo A >/dev/stderr
        local v="$(f2)"
        echo B >/dev/stderr
        return 0
    }

    set -e
    echo -n "main(): " >/dev/stderr
    set -o | grep errexit >/dev/stderr

    f1
    exit 0


Run this script by bash:

    $ bash ./t.sh  ; echo r=$?
    main(): errexit         on
    f1(): errexit           on
    A
    f2(): errexit           off
    subsh=1
    Failed
    B
    r=0

Despite the f2()'s non-zero return code, script have not terminated
immediately after f2() call.  Also, you may notice, that 'errexit' is not set
in f2() (this is because bash's non-standard behavior (see 'COMMAND EXECUTION
ENVIRONMENT' section in bash(1); this is only the case in _not_ posix mode).
If, though, i run this script by dash, 'errexit' will be inherited by subshell
spawned by command substitution, but f2()'s non-zero return code still does
not abort the script:

    $ dash ./t.sh  ; echo r=$?
    main(): errexit         on
    f1(): errexit         on
    A
    f2(): errexit         on
    subsh=
    Failed
    B
    r=0

Now, let's try to call f2() in variable assignment instead. f1() function will
then look like

    f1()
    {
        echo -n "f1(): " >/dev/stderr
        set -o | grep errexit >/dev/stderr
        echo A >/dev/stderr
        local v=''
        v="$(f2)"
        echo B >/dev/stderr
        return 0
    }


Run by bash:

    $ bash ./t.sh  ; echo r=$?
    main(): errexit             on
    f1(): errexit               on
    A
    f2(): errexit               off
    subsh=1
    Failed
    r=1

and by dash:

    $ dash ./t.sh  ; echo r=$?
    main(): errexit         on
    f1(): errexit         on
    A
    f2(): errexit         on
    subsh=
    Failed
    r=1

And both of them abort script immediately after f2() call. So, it seems, like
the problem is in `local` (i don't say this is bug).

Note1.

Let's also test bash's `declare` builtin. First call f2() from command
substitution in `declare` variable definition statement:

    set -e
    echo -n "main(): " >/dev/stderr
    set -o | grep errexit >/dev/stderr

    echo AAA >/dev/stderr
    declare v="$(f2)"
    echo BBB >/dev/stderr

    exit 0

Run by bash

    $ bash ./t.sh  ; echo r=$?
    main(): errexit             on
    AAA
    f2(): errexit               off
    subsh=1
    Failed
    BBB
    r=0

and the result is the same as with `local`. Now, call f2() from variable
assignment:

    set -e
    echo -n "main(): " >/dev/stderr
    set -o | grep errexit >/dev/stderr

    echo AAA >/dev/stderr
    declare v=''
    v="$(f2)"
    echo BBB >/dev/stderr

    exit 0

and run by bash

    $ bash ./t.sh  ; echo r=$?
    main(): errexit             on
    AAA
    f2(): errexit               off
    subsh=1
    Failed
    r=1

and the result is again the same as with `local` and now it works.