type declaration ignored when global variable is set

[stevengj]

var::T = val can be used to declare the type of a local variable, and it is enforced, but this is not true for global var::T = val.

For example, the following enforces the type:

julia> function foo(x)
          local y::Bool = x
       end
foo (generic function with 1 method)

julia> foo("hello")
ERROR: `convert` has no method matching convert(::Type{Bool}, ::ASCIIString)
 in foo at none:2

But this does not:

julia> y = false
false

julia> function foo(x)
          global y::Bool = x
       end
foo (generic function with 1 method)

julia> foo("hello")
"hello"

julia> y
"hello"

[JeffBezanson]

dup of #964