Add a build option for sanitizer.

This request relates to #835 and https://github.com/jubatus/jubatus_core/pull/29.

Usage:

```
./waf configure --fsanitize=memory
```

More than one sanitizer can be specified:

```
./waf configure --fsanitize=thread,undefined
```

Read http://clang.llvm.org/docs/UsersManual.html#controlling-code-generation for datails.