Added test for issue #14
Merge pull request #17 from nalimilan/master

Fix double ', case and period in load.ffdf()
Now that bug is fixed in package ff, get the overloading of [.ff and [<-.ff back in the package. And set minimal version to ff 2.2-11
Fix issue in documentation of table
Remove warning on request of Milan Bouchet-Valat
Remove opening/closing as these are now correctly handled in ff version 2.2-11
Fix for issue #18: bySum was not working correctly. (Thanks to @stevechc)
updating documentation
removed double entry
Fix merge.ffdf() when x and y contain identical column names

The column from y was discarded in that case. Also fix the code
so that in case of conflict suffixes are added to both x and y columns.
Find a shorter name for variables.
Fix ?merge.ffdf