queryparser/lemon.c: Sync change from upstream: "In LEMON, limit the
size of the grammar file to 100MB. This ensures that the program
will never experience integer overflow. To be doubly sure, use
calloc() instead of malloc() when allocating arrays." Generated code
is identical.

git-svn-id: file:///home/xapian-svn/xapian/trunk@18336 6b2f1b92-a4f3-0310-943f-de3cbe41748b