py-jinja2: updated to 2.10

Version 2.10:
- Added a new extension node called OverlayScope which can be used to
  create an unoptimized scope that will look up all variables from a
  derived context.
- Added an in test that works like the in operator.  This can be used
  in combination with reject and select.
- Added previtem and nextitem to loop contexts, providing access to the
  previous/next item in the loop. If such an item does not exist, the value is
  undefined.
- Added changed(*values) to loop contexts, providing an easy way of
  checking whether a value has changed since the last iteration (or rather
  since the last call of the method)
- Added a namespace function that creates a special object which allows
  attribute assignment using the set tag.  This can be used to carry data
  across scopes, e.g. from a loop body to code that comes after the loop.
- Added a trimmed modifier to {% trans %} to strip linebreaks and
  surrounding whitespace. Also added a new policy to enable this for all
  trans blocks.
- The random filter is no longer incorrectly constant folded and will
  produce a new random choice each time the template is rendered.
- Added a unique filter.
- Added min and max filters.
- Added tests for all comparison operators: eq, ne, lt, le,
  gt, ge.
- import statement cannot end with a trailing comma.
- indent filter will not indent blank lines by default.
- Add reverse argument for dictsort filter.
- Add a NativeEnvironment that renders templates to native Python types
  instead of strings.
- Added filter support to the block set tag.
- tojson filter marks output as safe to match documented behavior.
- Resolved a bug where getting debug locals for tracebacks could
  modify template context.
- Fixed a bug where having many {% elif ... %} blocks resulted in a
  "too many levels of indentation" error.  These blocks now compile to
  native elif ..: instead of else: if ..:

(adam)