bug#31092: 25.2: apropos-value: memory leak

[Boruch Baum]

In emacs version 25.2, in debian, I am reliably experiencing memory
exhaustion condition within five repeats of calls to function
`apropos-value'.

In the course of a cursory attempt to see what might be causing this, I
came across a curious global variable declaration `apropos-accumulator',
which doesn't look to be the culprit, but should be converted to a
locally scoped variable.

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