Fix find() when called with function and non-StridedArray

The previous code expected testfun to be vectorized, which does not match
the behavior of other methods, nor the documentation. Especially visible
when passing a sparse matrix. Always return an Array rather than an object
similar to the input, because it makes no sense to return a sparse vector.
Remove the method matching any object so that an error is raised rather
than returning incorrect results on non-AbstractArray (e.g. Set).
Update base.rst
Update helpdb.jl
Merge pull request #8376 from apeyser/master

 Suggestion: add to whos() documentation that it only displays exported variables #8375
deprecate randbool! and add rand(Bool). fixes #8377
Merge pull request #8323 from nalimilan/find

Fix find() when called with function and non-StridedArray