Let line/path support `shape` aesthetic (i.e., symbols)

* Fixes https://plot.ly/~TestBot/718/total-bill-vs-time/ (before: https://plot.ly/~ggplot2-cookbook/20)

* Add corresponding test (taken from R cookbook)

* Increment version number for this revision (now 0.5.2)

/cc @chriddyp @pedrodz