Add macro CAML_DEPRECATED(oldname,newname) to emit a deprecation warning
every time this macro is processed.

Use it to produce deprecation warnings when macros from <caml/compatibility.h>
are used.

Deprecate caml_aligned_malloc, caml_strdup and caml_strconcat from misc.h

If CAML_NAME_SPACE is not defined but CAML_INTERNALS is defined,
`alloc` is a compatibility macro that produces a warning when expanded.

The renaming to `allocated` is transparent, as all uses of this field
are through the `Chunk_alloc` macro.

This test exercises support for old, short names for runtime functions.
Now, it just triggers the new deprecation warning for these short names,
hence the test always fails.