Clarified comment on why memcpy perhaps wasn't being optimized to avoid call overhead.

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1074 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Removed "decreasing=" from radix orders and implemented "setrev" to reverse a vector by reference instead.

Tests added. NEWS item removed.

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1075 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added isolated fastorder.c for dev test

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1076 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Merge branch 'refs/heads/r-forge-git-svn-local'

Conflicts:
	pkg/src/init.c
Internal tweaks

Added:
  setreordervec' in C and wrapper in R for fast reordering of vectors
  argument 'o' to iradixorder, dradixorder, radixorder1 (all internal fns)
  tweaks to 'fastorder' - small performance improvement (using setreordervec)
  'chorder2' to be used internally for new tweaks to 'fastorder'
  tests for 'setreordervec'

Removed (minor):
  word 'inline' from Matthew's experimental forward-fastorder implementation

All internal changes - No NEWS updates.
'setkey' on already sorted DTs are almost instantaneous now.

Matthew's `isSortedList` (in C) makes this possible. Repeated 'setkey' or 'setkey' on data.tables that are already sorted are almost instantaneous now (Comparison on 1e8*2 DT, 55 sec vs 1.2 secs)