fix for posix semantics for the := word expansion when assigning array elements

tests/array30.sub

@@ -0,0 +1,46 @@
+#   This program is free software: you can redistribute it and/or modify
+#   it under the terms of the GNU General Public License as published by
+#   the Free Software Foundation, either version 3 of the License, or
+#   (at your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#   GNU General Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License
+#   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+declare -a a
+a=()
+
+echo ${a[42]=foo}
+declare -p a
+
+a=()
+echo ${a[$(echo 42)]=foo}
+declare -p a
+
+unset a
+
+declare -ai a
+a=()
+echo ${a[42]=4+3}
+declare -p a
+
+a=()
+echo ${a[$(echo 42)]=42}
+declare -p a
+
+unset a
+
+declare -A A
+declare -u A
+A=()
+echo ${A[$(echo Darwin)]=foo}
+
+declare -p A
+A=()
+
+echo ${A[@]:=foo}
+declare -p A