Regression in development version of bash w.r.t. associative hashes

[Stefano Lattarini]

[+cc bug-gnulib, see below for a reason]

Minimal reproducer of the regression:

  $ cat foo.bash
  echo "$BASH_VERSION"
  declare -A hash
  echo ${hash[a/b]}
  echo $?

  $ /bin/bash foo.bash
  4.2.45(1)-release

  0

  $ ~/bleeding/bin/bash foo.bash
  4.3.0(1)-alpha
  foo.bash: line 3: a/b: division by 0 (error token is "b")
  1

Notice that the new behaviour breaks the gnulib-tool script
(that's how I noticed this regression).

Regards,
  Stefano