Rework locale handling

Rework locale handling

 * Support all codepages, not just UTF-8 ones.

 * Although UTF-8 variants are still preferred, specifying an invalid
   codepage as an extension to a known language will not necessarily result
   in en_US.UTF-8 being chosen - it will try and use an alternate.

 * Fixes an issue whereby an unknown locale would end up as a blank
   "language" in /etc/kde3/kdm/kdmrc instead of en_US.

 * General tidying of the code.

Signed-off-by: Chris Lamb <chris@chris-lamb.co.uk>