Minor change: No need to specify the namespace of raw_ostream.

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@185252 91177308-0d34-0410-b5e6-96231b3b80d8
Refactor memory access getting code in ScopStmt.

1. Do not allow creating new memory access record in the InstructionToAccess map
   on the fly in function getAccessFor.
2. Do not allow user to modify the memory accesses returned by getAccessFor
   during the code generation process.

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@185253 91177308-0d34-0410-b5e6-96231b3b80d8