languages/: Generate a compact and efficient table to convert
language names to enum codes, which we can then use a C switch
statement to dispatch.  The table first checks the token length,
and then does a binary chop on tokens of the same length.  This
is both faster and smaller than the approach we were using, with
the benefit that the table is auto-generated.

git-svn-id: file:///home/xapian-svn/xapian/trunk@17046 6b2f1b92-a4f3-0310-943f-de3cbe41748b