Make indexin first argument accept iterables as well

I also fixed the docstring and added a test where a matrix is passed.

Also compactified the tests according to
https://github.com/JuliaLang/julia/pull/8622/files#r18615289

base/array.jl

@@ -2201,8 +2201,8 @@ indmin(a) = findmin(a)[2]
 """
     indexin(a, b)
 
-Returns a vector containing the highest index in `b` for
-each value in `a` that is a member of `b` . The output
+Returns an array containing the highest index in `b` for
+each value in `a` that is a member of `b`. The output
 vector contains 0 wherever `a` is not a member of `b`.
 
 # Examples
@@ -2227,7 +2227,7 @@ julia> indexin(b,a)
  3
 ```
 """
-function indexin(a::AbstractArray, b::AbstractArray)
+function indexin(a, b::AbstractArray)
     bdict = Dict(zip(b, 1:length(b)))
     [get(bdict, i, 0) for i in a]
 end

test/arrayops.jl

@@ -1370,13 +1370,10 @@ function i7197()
 end
 @test i7197() == (2,2)
 
-# PR #8622 and general indexin test
-function pr8622()
-    x=[1,3,5,7]
-    y=[5,4,3]
-    return indexin(x,y)
-end
-@test pr8622() == [0,3,1,0]
+# PR #8622 and general indexin tests
+@test indexin([1,3,5,7], [5,4,3]) == [0,3,1,0]
+@test indexin((2 * x + 1 for x in 0:3), [5,4,3]) == [0,3,1,0]
+@test indexin([1 3; 5 7], [5 4; 3 2]) == [0 2; 1 0]
 
 #6828 - size of specific dimensions
 let a = Array{Float64}(10)