Clean sourcepos records when they come from metadata.

[dmurdoch]

NB: the sourcepos records refer to the intermediate .md file, not the .Rmd file. I'll be updating the RmdConcord package to correct these based on the knitr concordance record.

I looked into the possibility of keeping the metadata sourcepos records, but it's just too much trouble.

[yihui]

Perfect. Thanks!

[dmurdoch]

Just a note to say that the RmdConcord package v 0.3 now supports html_format documents (using the RmdConcord::html_formatC name), and has been accepted on CRAN. It requires markdown version 1.12.1 or higher (i.e. this PR) to do anything; it'll just give a warning if you try to use it with an older version. This means that check warnings from tidy_validate can be connected back to the source line in the Rmd file.

[yihui]

Thanks for the heads up! The next version of markdown may be released in January next year.