Made animframe_polyfill.js JSHint compliant

There's a few more errors, but those would require more in-depth refactors.

JSHint results:
```
> jshint js/*
animframe_polyfill.js: line 1, col 10, Missing space after 'function'.
animframe_polyfill.js: line 4, col 6, Missing space after 'for'.
animframe_polyfill.js: line 5, col 53, Missing space after ']'.
animframe_polyfill.js: line 5, col 54, Missing space after '+'.
animframe_polyfill.js: line 7, col 98, Line is too long.
animframe_polyfill.js: line 7, col 22, Missing space after ']'.
animframe_polyfill.js: line 7, col 23, Missing space after '+'.
animframe_polyfill.js: line 7, col 67, Missing space after ']'.
animframe_polyfill.js: line 7, col 68, Missing space after '+'.
animframe_polyfill.js: line 11, col 44, Missing space after 'function'.
animframe_polyfill.js: line 14, col 81, Line is too long.
animframe_polyfill.js: line 14, col 42, Missing space after 'function'.
animframe_polyfill.js: line 22, col 43, Missing space after 'function'.
animframe_polyfill.js: line 11, col 62, 'element' is defined but never used.

bind_polyfill.js: line 1, col 19, Extending prototype of native object: 'Function'.

game_manager.js: line 263, col 52, Blocks are nested too deeply. (5)

16 errors
```