use version rather than longer form

Merge branch 'master' of github.com:rstudio/rstudio

support "auto" option for cores

pass commit mode parameter to alternate chunk execution engines

run restart-prefixed notebook commands in current window

apply R Markdown front matter more selectively/efficiently

This change includes two improvements to dealing with front matter:
- The front matter is now extracted more efficiently. The entire
  document is not flattened; instead, we read only as many lines as
  necessary.
- More importantly, only the region of the document containing the front
  matter is changed when the front matter is modified; this fixes some
  bugs that occur when swapping out the entire document's contents, and
  makes undo perform more reasonably.

better name

better name

better name

implement chunk interrupt handling for non-R chunks