We're starting to see a mix between uses of zend_bool and bool.
Replace all usages with the standard bool type everywhere.
Of course, zend_bool is retained as an alias.
This is simpler than going through curl, because we can manage
the memory more easily (in particular, this removes the need for
to_free->str). Additionally this allows the CURLOPT_PRIVATE data
to have any type, instead of being implicitly cast to string.
For these callbacks a non-null callback already indicates that
a user callback should be used. We don't need an additional
member to tell us the same thing.
Not keeping a reference will not result in use after free, because
curl protects against it, but it will result in a memory leak,
because curl_share_cleanup() will fail. We should make sure that
the share handle object stays alive as long as the curl handles
use it.
To allow exporting the php_curl.h header containing curl class
entries, split off a separate curl_private.h header with all the
implementation details.
We may move or expose additional APIs in php_curl.h on an as-needed
basis.
