Fix issues with initializers for let/const.

Fix issues with initializers for let/const.

BUG=http://code.google.com/p/traceur-compiler/issues/detail?id=29
TEST=test/feature/Classes/Error_ConstMissingInitializer.js
     test/feature/Scope/Error_ConstMissingInitializer.js
     test/feature/Scope/Error_ForInWithInitializerConst.js
     test/feature/Scope/Error_ForInWithInitializerLet.js
     test/feature/Scope/Error_ForOfWithInitializerConst.js
     test/feature/Scope/Error_ForOfWithInitializerLet.js
     test/feature/Scope/Error_ForOfWithInitializerVar.js
     test/feature/Scope/Error_ForWithoutInitializerConst.js
     test/feature/Scope/ForInWithInitializerVar.js
     test/feature/Scope/LetNoInitializer.js
     test/feature/Scope/LetNoInitializerGlobal.js

Committed: http://code.google.com/p/traceur-compiler/source/detail?r=343

[arv, 2011-10-28 05:49:17]

https://codereview.appspot.com/5314063/diff/1/src/syntax/Parser.js
File src/syntax/Parser.js (left):

https://codereview.appspot.com/5314063/diff/1/src/syntax/Parser.js#oldcode1530
src/syntax/Parser.js:1530: this.reportError_('const variables must have an
initializer');
This now gets checked in the construct that uses the variable since there are
cases where const should not take an initializer.

https://codereview.appspot.com/5314063/diff/1/src/syntax/Parser.js#oldcode1712
src/syntax/Parser.js:1712: (variables.declarationType == TokenType.LET ||
Only CONST needs an initializer.

[cburrows, 2011-10-31 06:53:36]

LGTM

[slightlylate, 2011-10-31 15:20:34]

LGTM