More uses of macros 'likely'/'unlikely' (renamed to
'l_likely'/'l_unlikely'), both in range (extended to the
libraries) and in scope (extended to hooks, stack growth).

Names in the parser and other details that do not change actual code.

That optimization was too complex and caused some weird traces when
debugging. The more common case «if ... then break» was kept.

- more organized handling of 'nCcalls'
- comments
- deprecation of 'setcstacklimit'

A "with stack" implementation gains too little in performance to be
worth all the noise from C-stack overflows.

This commit is almost a sketch, to test performance. There are several
pending stuff:

- review control of C-stack overflow and error messages;
- what to do with setcstacklimit;
- review comments;
- review unroll of Lua calls.

While building a new prototype, the GC needs barriers for every object
(strings and nested prototypes) that is attached to the new prototype.

The parser were mixing compiler indices of variables with stack indices,
so that when a to-be-closed variable was used inside the scope of
compile-time constants (which may be optimized away), it might be closed
in the wrong place. (See new tests for examples.)

Besides fixing the bugs, this commit also changed comments and variable
names to avoid that kind of confusion and added tests.