.arcconfig

revsetlang: do not pass in non-bytes to parse()

Since parse() isn't a simple function, we shouldn't expect it would raise
TypeError or ValueError for invalid inputs. Before, TypeError was raised
at 'if pos != len(spec)', which was quite late to report an error.

This patch also makes tokenize() detect invalid object before converting
it to a py3-safe bytes.

Spotted while adding the 'revset(...)' hack to _parsewith().

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