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.
numerous issues fixed:
* buffer overflows
* error conditions aren't checked (crash if file doesn't exist)
* accessing random unallocated memory
* hard-coded password
* arbitrary hard-coded key id limit
* incomprehensible error messages (for key_id == 0 it reported
"The key could not be initialized", for syntax errors the message was
"Wrong match of the keyID, see the template", for a key id
larger than hard-coded limit the message was "No asked key", and there
was an error "Is comment" for a comment).
* tons of small mallocs, many are freed few lines down in the code
* malloc(N) and new char[N] are used both, even in the same function
* redundant memory copies
* pcre - "I can solve it with regular expressions" - with incorrect regexes
* parser context stored in a singleton
* keys are stored as strings and are strlen-ed and hex2bin-ed on every
get_key() request
* lots of useless code (e.g. sprintf instead of a pointer assignment,
checking of the file length to read a part of it in a fixed buffer,
multiplying by sizeof(char) in many places, etc)
* this list is not exhaustive
