ash: Expand here-documents in the current shell environment

ash: Expand here-documents in the current shell environment

Upstream commit:

    Date: Sun, 11 Nov 2007 15:27:00 +0800
    Expand here-documents in the current shell environment

    Previously we always expanded here-documents in a subshell.  This is
    contrary to the POSIX specification and how other shells behave.  What's
    more this slows down many expansions due to the extra fork (however, it
    must be said that it is possible for it speed up certain expansions by
    running it simultaneously with the command on two CPUs).

    This patch move the expansion into the current shell environment.

    Test case:

            unset a
            cat <<- EOF > /dev/null
                    ${a=NOT}
            EOF
            echo ${a}BAD

    Old result:

            BAD

    New result:

            NOTBAD

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>