[Pullrequest] Better error message for non-existing chart conversion
Created by: tobiasdiez
I had some problems debugging an error that resulted from non-existing chart conversions. I created a fix at https://github.com/sagemath/sage/pull/65. But this github rep is read-only so I was referred to http://trac.sagemath.org/ . For some reason, I'm too stupid to create a PR using trac. Thus this message to inform you about my proposed changes. If you feel like that these are valuable, feel free to include them. Thanks for developing SageManifolds!