Replace usage of safe-bool idiom with explicit conversion operator
* src/global.h (GPGMEPP_MAKE_SAFE_BOOL_OPERATOR): Remove. * src/configuration.h (class Component, class Option, class Argument): Replace "safe bool operator" with explicit operator bool. * src/error.h (class Error): Ditto.
With C++11 we can use an explicit conversion operator to implement
operator bool in a safe way.