Std: add (@@) operator (not available in 4.00)
Merlin_typer: with_typer no longer capture errors

Use protect_typer to capture errors. This fix a regression introduced
during typer simplification.
Command: uniformize use of (@@)

When it decreases indentation :P
vim: move all buffer init into merlin#Register
vim: don't load merlin in *merlin-type-history*
vim: clear *merlin-type-history* before adding new type
Type_utils: make type expansion recursive
Typing_aux: add uncatch_errors to reenable type errors locally
Type_utils: detect type errors and fallback to other cases