use name in source module when importing an aliased binding

This solves the following problem:
```julia
julia> module A
           import Base.identity as id
       end
Main.A

julia> import .A.id

julia> id
ERROR: UndefVarError: id not defined
```

src/module.c

@@ -528,7 +528,7 @@ static void module_import_(jl_module_t *to, jl_module_t *from, jl_sym_t *s, jl_s
             }
         }
         else {
-            jl_binding_t *nb = new_binding(s);
+            jl_binding_t *nb = new_binding(b->name);
             nb->owner = b->owner;
             nb->imported = (explici!=0);
             nb->deprecated = b->deprecated;

test/syntax.jl

@@ -2503,6 +2503,7 @@ end
 end
 
 module Mod2
+import ..Mod.x as x_from_mod
 const y = 2
 end
 
@@ -2543,6 +2544,11 @@ import .Mod.@mac as @m
 @test_throws ErrorException eval(:(import .Mod.func as @notmacro))
 @test_throws ErrorException eval(:(using .Mod: @mac as notmacro))
 @test_throws ErrorException eval(:(using .Mod: func as @notmacro))
+
+import .Mod2.x_from_mod
+
+@test @isdefined(x_from_mod)
+@test x_from_mod == Mod.x
 end
 
 import .TestImportAs.Mod2 as M2