Make sure that SimpleLists are coerced to a DataFrame with a single
column. The methods package was trying to create a DataFrame with one
column per element, because DataFrame extends SimpleList.


git-svn-id: https://hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/IRanges@76895 bc3139a8-67e5-0310-9ffc-ced21a209358
push isEmpty up to List, from Simple/CompressedList; seems like a
general property of all lists.


git-svn-id: https://hedgehog.fhcrc.org/bioconductor/trunk/madman/Rpacks/IRanges@76896 bc3139a8-67e5-0310-9ffc-ced21a209358
Merge branch 'local-hedgehog'