behavior of local functions is incorrect in v0.5

[josefsachsconning]

I don't see an explanation in NEWS.md for this change in behavior, so I am considering it a bug.

C:\>julia
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.4.5 (2016-03-18 00:58 UTC)
 _/ |\__'_|_|_|\__'_|  |  Official http://julialang.org/ release
|__/                   |  x86_64-w64-mingw32

julia> function foo(val::Int64)
           if val == 1
               function bar()
                   return 100
               end
           elseif val == 2
               function bar()
                   return 200
               end
           end
           return bar()
       end
foo (generic function with 1 method)

julia> foo(1)
100

julia> foo(2)
200

julia> exit()

C:\>"C:\Program Files\Julia-0.5.0-rc3\bin\julia.exe"
               _
   _       _ _(_)_     |  A fresh approach to technical computing
  (_)     | (_) (_)    |  Documentation: http://docs.julialang.org
   _ _   _| |_  __ _   |  Type "?help" for help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 0.5.0-rc3+0 (2016-08-22 23:43 UTC)
 _/ |\__'_|_|_|\__'_|  |
|__/                   |  x86_64-w64-mingw32

julia> function foo(val::Int64)
           if val == 1
               function bar()
                   return 100
               end
           elseif val == 2
               function bar()
                   return 200
               end
           end
           return bar()
       end
WARNING: Method definition bar() in module Main at REPL[1]:4 overwritten at REPL[1]:8.
foo (generic function with 1 method)

julia> foo(1)
200

julia> foo(2)
200

[cstjean]

It's #15602