Incorrect circle example for callcc

[airstone42]

context/example/callcc/circle.cpp

Line 21 in eb7c047

f2 = f1.resume();

It failed to compile as resume() was rvalue-ref qualified.

context/example/callcc/circle.cpp

Line 11 in eb7c047

#include <boost/context/fiber.hpp>

It seems that this example was supposed to use callcc while it uses fiber now, which duplicates with example/fiber/circle.cpp.

[olk]

ty, fixed