Fixing fcast

Trying out fix for fcast segfault

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1093 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Fix for dcast segfault

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1094 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
In fastorder, groups from counting step are now reused to save x[i]==x[i-1] (and access to x at all) when building subgroups.

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1095 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Merge branch 'refs/heads/r-forge-git-svn-local'