Fix #340: build DevFailed origin from format_exception instead of for…
The DevFailed.origin text is being build from the inspect.format_tb() function With this PR I propose to build it from inspect.format_exception(). This way the full exception information is seen as requested by #340 (closed)
This introduces an incompatibility if someone is parsing the DevFailed.origin error to do fancy stuff. I don't think anyone is crazy enough to do it but just in case here is the warning.