Circular dependency

[NeilFraser]

The advanced compilation test fails:

$ ./compile.sh 
Compiling Blockly...
../../blocks/logic.js:449: WARNING - Redeclared variable: i
    for (var i = 1; i <= this.elseifCount_; i++) {
             ^^^^^

../../core/block.js:1120: WARNING - Redeclared variable: i
    for (var i = 0; i < extensionNames.length; ++i) {
             ^^^^^

../../core/field_variable.js:301: WARNING - Redeclared variable: variableModelList
    var variableModelList = [];
        ^^^^^^^^^^^^^^^^^^^^^^

../../core/generator.js:30: ERROR - required "Blockly.Block" namespace not provided yet
goog.require('Blockly.Block');
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1 error(s), 3 warning(s)
Compilation FAIL.

This also breaks Blockly Games.

[rachel-fenichel]

https://github.com/google/blockly/blob/develop/core/block.js#L33

@AnmAtAnm

Removing that line fixes compilation.