Remove unused CHPL_RT_MD types:

- CHAPEL_CODE
- GC_HEAP
- GC_SPACE_POINTER
- FLAG_SERIAL
Added a bug future on a missing const check
Merge pull request #117 from chapel-lang/addRecordArgConstCheckingFuture

Added a bug future on a missing constness check.

From .future: an assignment to a field of a record-typed formal passed by blank intent is not flagged as an error.

Constness checking implemented in SVN r22963 needs to be extended to
report an error in this code. That's because since a record passed
by blank intent is considered "const", it should not be assignable.

proc myProc(y: MyRecord) {
  y.myField = 7;   <--- should be an error                                                                                       
  writeln(y);
}

Thanks to Tim Z for bringing this to my attention.
Merge pull request #116 from sungeunchoi/test

Remove unused memory descriptor types

[reviewed by Tom]

This commit removes the following unused memory descriptor types:

- CHAPEL_CODE
- GC_HEAP
- GC_SPACE_POINTER
- FLAG_SERIAL

There are a few remaining unused types, but they seemed like they may be useful in the future (or were possibly not used on accident) as they are related to other descriptors that are used, so I left them in there.