Add a prefix "xclip::Error" with the error message so that the user can know what program is causing the error.
Print the id of the owner of the selection in the verbose mode so that the developer can know what program cannot fulfill the request of ConvertSelection.
Fix the issue #38 (https://github.com/astrand/xclip/issues/38).
Add a prefix "xclip::Error" with the error message so that the user can know what program is causing the error. Print the id of the owner of the selection in the verbose mode so that the developer can know what program cannot fulfill the request of ConvertSelection.