+ by=.JOIN replaces by-without-by
+ consistent "i." prefixes in j
+ more verbose timing in dogroups and setkey
+ 0 and NA now silently skipped in i of := and set()
+ X[Y,colA] now returns a vector, for consistency with documentation
+ X[Y] keeps X's join column in place rather than moving to the front

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1231 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
NEWS item and test for consistency of mult="all" vs "first"|"last" output type and columns, #5378

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1232 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
.JOIN changed to .EACHI

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1233 edb9625f-4e0d-4859-8d74-9fd3b1da38cb