PROTON-558: Rearrange FIELD table to save space:
- Splitting the table into 2 string tables
  and just put table offsets in the actual FIELD table.
- Make tables constant to give them a chance to get into
  the program text
- Add error checking to make sure we don't access the wrong
  field name or a null.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1595306 13f79535-47bb-0310-9956-ffa450edef68