Case 3 does not work (in examples) for download.datasets(.) for multiple datasets

[QuantDevHacks]

This is a follow-on issue to issue #95. Cases 1 and 2 (see frame1 and frame2 in function help) now work when the name argument consists of either a single dataset or multiple datasets. Case 3; viz,

 # Note that one can examine all the names, sizes, etc. of the datasets
  # in ws by examining d:
  d <- datasets(ws)
  frame3 <- download.datasets(subset(d, Name == name))

where there is the single argument, works if name consists of a single dataset but fails if more than one are included. Will close out #95 and isolate the remaining work to be done in this issue.

[QuantDevHacks]

A change has been made to the documentation indicating that the frame3 <- download.datasets(subset(d, Name == name)) example only currently works with a single dataset. The problem actually lies here: subset(d, Name == name) ie, it seems (perhaps) the subset function has not been properly overloaded for the case where d is a Datasets object. Will mark this issue as done and open an new issue that focuses on the subset(.) function specifically.

[andrie]

Fixed in #111