Fix functionExpression() incorrectly prohibiting the use of an identifier as in:

var f = function foo() { ... }

As specified in http://www.ecma-international.org/ecma-262/5.1/#sec-13 this syntax is valid (the identifier being optional).
Add jasmine spec test to validate fix.
Merge pull request #123 from malaporte/fix-function-expression-with-identifier

Fix functionExpression() incorrectly prohibiting the use of an identifier