RELEASE_3_5_10: Cleanup a bit ipython code that displays figures. (#1003)

Release 3.5.10

New features

• :mod:rpy2.situation reports cffi interface type information.

• The ipython/jupyter R magic can now have jpeg as a default graphics format
  for static figures in addition to png and svg.

Bugs fixed

• Building the path to the R shared library was incorrectly
  using the output of R CMD config LIBnn (issue #982).

• R started raising warnings when calling formals on BUILTINSXP R objects.
  Internal functions in :mod:rpy.robjects.functions calling formals no
  longer propagate the warnings.