Compile with -Werror and -Wall (#1116)

* Compile global scheduler with -Werror -Wall.

* Compile plasma manager with -Werror -Wall.

* Compile local scheduler with -Werror -Wall.

* Compile common code with -Werror -Wall.

* Signed/unsigned comparisons.

* More signed/unsigned fixes.

* More signed/unsigned fixes and added extern keyword.

* Fix linting.

* Don't check strict-aliasing because Python.h doesn't pass.

src/common/lib/python/common_extension.h

@@ -8,7 +8,7 @@
 #include "common.h"
 
 typedef uint8_t TaskSpec;
-struct TaskBuilder;
+class TaskBuilder;
 
 extern PyObject *CommonError;