Fix issue #3132 : Array of structs (and rm white-space)

Before commit : 
```
class Test
{
    static function main()
    {
        [{a:1}, {a:1, b:2}]; //ok
        [{a:1, b:2}, {a:1}]; //error: Arrays of mixed types are only allowed if the type is forced to Array<Dynamic>
    }
}
```
After : 
```
class Test
{
    static function main()
    {
        [{a:1}, {a:1, b:2}]; // error: Arrays of mixed types are only allowed if the type is forced to Array<Dynamic>
        [{a:1, b:2}, {a:1}]; //error: Arrays of mixed types are only allowed if the type is forced to Array<Dynamic>
    }
}
```
Just test if structs have same number of fields and raise an error if not. (Not sure if this commit will have side-effects on regressions tests)