Core is supposed to be the most basic library, providing only
really common features used everywhere like fiber, diag, memory,
logging. Which can't be said about collations - they are used
only by high level things - SQL, Lua utf8, comparators.

Collations are built now as 'lib/coll' library.

The patch is not necessary for anything, but it is a right thing
to do, while some activity is happening there.