OpenSSL changes in PHP 5.6.x
New global constants
Migrating from PHP 5.5.x to PHP 5.6.x
PHP Manual

## Other changes to extensions

### cURL

A number of constants marked obsolete in the cURL library have now been removed:

- `CURLOPT_CLOSEPOLICY`
- `CURLCLOSEPOLICY_CALLBACK`
- `CURLCLOSEPOLICY_LEAST_RECENTLY_USED`
- `CURLCLOSEPOLICY_LEAST_TRAFFIC`
- `CURLCLOSEPOLICY_OLDEST`
- `CURLCLOSEPOLICY_SLOWEST`

### OCI8

- Support for implicit result sets for Oracle Database 12c has been added via the new oci_get_implicit_resultset() function.
- Using oci_execute($s, OCI_NO_AUTO_COMMIT) for a SELECT no longer unnecessarily initiates an internal ROLLBACK during connection close.
- Added DTrace probes controlled by the --enable-dtrace configure option.
- oci_internal_debug() is now a no-op.
- The phpinfo() output format for OCI8 has changed.

### Zip

A --with-libzip configure option has been added to use a system libzip installation. libzip version 0.11 is required, with 0.11.2 or later recommended.

### MySQLi

A new mysqli.rollback_on_cached_plink option was added to rollback connections put back into the persistent connection pool.

OpenSSL changes in PHP 5.6.x
New global constants
Migrating from PHP 5.5.x to PHP 5.6.x
PHP Manual