Implement RFC: Introduce session_start() options - read_only, unsafe_lock, lazy_write and lazy_destroy

UPGRADING

@@ -85,6 +85,18 @@ PHP X.Y UPGRADE NOTES
   . gmp_setbit() and gmp_clrbit() now return FALSE for negative indices, making
     them consistent with other GMP functions.
 
+- Session
+  . session_start() accepts all INI settings as array. e.g. ['cache_limiter'=>'private']
+    sets session.cache_limiter=private. It also supports 'read_and_close' which closes
+    session data immediately after read data.
+  . Save handler accepts validate_sid(), update_timestamp() which validates session
+    ID existence, updates timestamp of session data. Compatibility of old user defined
+    save handler is retained.
+  . SessionUpdateTimestampHandlerInterface is added. validateSid(), updateTimestamp()
+    is defined in the interface.
+  . session.lazy_write(default=On) INI setting enables only write session data when
+    session data is updated.
+
 - PCRE:
   . Removed support for /e (PREG_REPLACE_EVAL) modifier. Use
     preg_reaplace_callback() instead.

UPGRADING.INTERNALS

@@ -204,3 +204,22 @@ PHP 7.0 INTERNALS UPGRADE NOTES
      - configure.js now produces response files which are passed to the linker
        and library manager. This solves the issues with the long command lines
        which can exceed the OS limit.
+
+
+========================
+3. Module changes
+========================
+
+  Session:
+
+    - PS_MOD_UPDATE_TIMESTAMP() session save handler definition is added. New
+      save handler should use PS_MOD_UPDATE_TIMESTAMP() definition. Save handler
+      must not refer/change PS() variables directly from save handler.
+    - PS_MOD_UPDATE_TIMESTAMP() defines validate_sid() handler. This handler
+      must validate if requested session ID is in session data storage or not.
+      Internal save handler needed to asscess PS(id) directly to validate it.
+      Do not access PS(id), but use this handler.
+    - PS_MOD_UPDATE_TIMESTAMP() defines update_timestamp() handlers. This handler
+      must update session data timestamp for GC if it is needed. e.g. Memcache
+      updates timestap on read, so it does not need to update timestamp. Return
+      SUCCESS simply for this case.