Do not exporting mysqld entry points directly.
This is needed for mariabackup, to load encryption plugins on Windows.

All plugins are "pure" by default. To mark plugin "impure"
it should use RECOMPILE_FOR_EMBEDDED or STORAGE_ENGINE keyword.

Added service for
- encryption (AES)
- error reporting, e.g my_printf_error()

Instead of encrypt(src, dst, key, iv) that encrypts all
data in one go, now we have encrypt_init(key,iv),
encrypt_update(src,dst), and encrypt_finish(dst).

This also causes collateral changes in the internal my_crypt.cc
encryption functions and in the encryption service.

There are wrappers to provide the old all-at-once encryption
functionality. But binlog events are often written piecewise,
they'll need the new api.

show that two keys can be different if they have different ids
or different versions.

that for some reasons worked on linux, but crashed on windows

which is separate from the encryption key version

with namespace prefixes