Refactoring from std::ostream to llvm::raw_ostream

According to LLVM: lightweight and simpler implementation of streams.
Remove #include <iostream> to avoid static constructors

iostream injects static constructor function into every compilation unit.
Remove this to avoid it.
Avoid non-explicit use of functions from std namespace in KLEE
Fix header
Use LLVM DEBUG macro instead of #if 0 or #if DEBUG
Fix ExprTest under LLVM 2.9
Merge pull request #117 from MartinNowack/llvm_raw_ostream

Refactor std::ostreams to llvm::raw_ostream and minor cleanups