Squashed commit of the following:

Fix for #5266 and #5159 - character encodings
    `chmatch` and joins on character columns now work as expected on different encodings as well.

Updated 'fcast' + minor edits to 'fmelt'
    'fcast' updated to handle recent changes to 'fastorder' (used internally) + minor renaming to fmelt functions.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1091 edb9625f-4e0d-4859-8d74-9fd3b1da38cb