base: Rewrite the CircleBuf to fix bugs and add serialization

The CircleBuf class has at least one bug causing it to overwrite the
wrong elements when wrapping. The current code has a lot of unused
functionality and duplicated code. This changeset replaces the old
implementation with a new version that supports serialization and
arbitrary types in the buffer (not just char).

src/base/SConscript

@@ -37,7 +37,6 @@ Source('atomicio.cc')
 Source('bigint.cc')
 Source('bitmap.cc')
 Source('callback.cc')
-Source('circlebuf.cc')
 Source('cprintf.cc')
 Source('debug.cc')
 if env['USE_FENV']: