Various fixes (squashed commit).

Fix for #5190

>> Arose while implementing FR #4979. When grouping with .SDcols argument value as a variable, it lead to an error "symbol not subsettable". This is now fixed. Tests added and NEWS updated.

>> duplicated.data.table (and therefore unique.data.table) is now 10-12x faster than 1.8.10 due to 2 factors: 1) fast order 2) removal of an unnecessary ordering in code. Updated NEWS. No tests added.

>> Fixed a nasty bug in 'rlixlist' that lead a segfault in some cases.  No test added yet (it was a set fault on certain data).

This is a squashed commit. Check https://github.com/arunsrinivasan/datatable for individual commits.

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1049 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Squashed commit of the following:

Fix for #5171 - Fixed a segfault when the attribute name to `setattr` is not of type character. returns a friendly error instead.

Minor: changed "molten" to "cast" in fcast.R info message.

Fixes #5150 - Use of R_xlen_t on <3.0.0 R versions will lead to compilation error. Added a smart version check to get R version and use R_xlen_t or R_len_t accordingly.

Updated '?setkey' reg. the new radix orders.

rlixlist is now uniqlist + uniqlengths - Changed `data.table.R`, `duplicated.R` and `tests.Raw` to reflect these changes. Tested successfully and modified NEWS accordingly.

Binary search NA/NaN fix (also fixes #4918) - Binary search can now subset, join and merge on NA/NaN values as well. Note that NA and NaN are not identical for any of these operations. DT[J(NA_real_)] for ex: subsets all columns corresponding to NA_real_ key column.

Minor: changed fastorder to reflect the correct message of order being called when base's radix order fails.

"decreasing=T/F" argument for radix order - radix order for int and double can now order (or sort) in decreasing order - preparation for changing DT[order(..)] to DT[fastorder(…)] in 'i'.

Forgot to commit NEWS.

Tests added and tested successfully. NEWS updated. Squashed commit. See https://github.com/arunsrinivasan/datatable/commits/master for info reg. individual commits.

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1050 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Minor bug fix in binary search NA/NaN

Fixed a case where 'i' has NaN to search for from 'x' with both 'NA' and 'NaN'. Added test.

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1051 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Uploaded Cologne R presentation.

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1052 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Merge https://github.com/arunsrinivasan/datatable