Without this change, classes (including iclass) are allocated
as un-boxable classes after initializing user boxes (after starting
script evaluation). Under this situation, iclasses are created as
un-boxabled class when core modules are included by a class in the
root box, then it causes problems because it's in the root box but
it can't have multiple classexts.

This change makes it possible to allocate boxable classes even after
initializing user boxes. Classes create in the root box will be
boxable, and those can have 2 or more classexts.

It is impossible to delete DLLs being loaded on Windows.  I guess that
unnamed (no accessible path on the filesystem) files are not allowed
essentially.  The only way is to relax the condition, such as no files
are left after the process terminated, probably.

Re-organize page docs