Annotations lead to internal errors

[marcoeilers]

The following program

method m()
{
    assert @someAnn("hello") false
}

leads to internal errors:

carbon found 2 errors in 1.31s:
  [0] An internal error occurred. Found an unparsable output from Boogie: stdin.bpl(201,60): error: "}" expected (<no position>)
  [1] An internal error occurred. Found an unparsable output from Boogie: 1 parse errors detected in stdin.bpl (<no position>)