Fix for #5171

Fixed a segfault when the attribute name to `setattr` is not of type character. returns a friendly error instead.
NEWS updated. Tested successfully.
minor fix

Minor: changed "molten" to "cast" in fcast.R info message.
Fixes #5150 - R_xlen_t and R_len_t Rversion fix in Rbindlist.c

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.
minor - marked bug number in rbindlist.c

Added "fix for #5150" in rbindlist.c for future reference.
Changed documentation for setkey

Added changes to order in setkey help page.
rlixlist -> uniqlist + uniqlengths

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

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.

This also fixes bug #4918. Tests added for both and tested successfully. NEWS updated.
minor fix

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'.
Tests added and tested with success. NEWS updated.
Forgot to commit NEWS.