parser: 'let' expressions can't be used as arguments to function call (several problems)

[lth]

Consider f(let (x = 10) new Object), which is valid code. This fails in various ways:

>> f(let (x = 10) new Object)
**ERROR** ParseError: unknown token in argumentList
>> f((let (x = 10) new Object))
[object Object]
>> f(let (x = 10) (new Object))
**ERROR** EvalError: uncaught exception:
  ReferenceError: unresolved lexical reference
  {multiname: [ns public '']::let
              [ns internal '']::let
              [ns intrinsic]::let }

[lth]

See also #144.

Same problem with function expressions:

[1,2,3].map(function (x) x*2)

**ERROR** ParseError?: unknown body form in anonymous function expression

[1,2,3].map((function (x) x*2))

2,4,6

[graydon]

Appears fixed in recent revs, not sure which.