PlaceholderParser: handle arrays of statements, expressions, etc.

PlaceholderParser: handle arrays of statements, expressions, etc.

- Arrays of statements converted to a block statement.
- Arrays of expressions converted to a comma expression.
- Arrays converted to an array literal.

BUG=None
TEST=None

[usrbincc, 2013-03-21 21:19:33]

A lot of State functions return arrays of statements, so I added this to
make integration with PlaceholderParser easier. The other functionality
was easy to implement, so I added it in.

#--cut--
dl_check() {
  local f=$(basename $1)
  test -e $f || curl -sO $1
  openssl sha1 < $f | grep -q "= $2" && return 0
  echo sha1 mismatch!
  return 1
}

git checkout 60408908bf3c682b   # last merge with branch master

git checkout -b issue7649045-placeholder-parser-statement-arrays

dl_check https://codereview.appspot.com/download/issue7649045_1.diff \
  a1de2b3be3fc2dde && git apply issue7649045_1.diff && make test

node demo/repl.js <<"END"
var ps = traceur.codegeneration.parseStatement;
var pe = traceur.codegeneration.parseExpression;
var w = traceur.outputgeneration.TreeWriter.write;

console.log(w(ps`var a = ${[pe`3+4`, pe`5+6`]}`));
console.log(w(ps`if (i < n) ${[ps`i++;`, ps`break;`]}`));
console.log(w(ps`var v = ${
  'hello world'.split('').map((c) => c.charCodeAt(0))
}`));
END
#--cut--

[arv, 2013-03-21 21:45:34]

LGTM

[arv, 2013-03-21 21:47:08]

Committed as bbe258db9a5e993d33732cbf328b17a9b38e4240