Previous code incorrectly assumed that nodes with identical keys are linked
together.  This might not be true after tree rebalance.

Patch by Lanshun Zhou.

With previous code raw buffer might be lost if p->input_filter() was called
on a buffer without any data and used ngx_event_pipe_add_free_buf() to
return it to the free list.  This eventually might cause "all buffers busy"
problem, resulting in segmentation fault due to null pointer dereference in
ngx_event_pipe_write_chain_to_temp_file().

In ngx_event_pipe_add_free_buf() the buffer was added to the list start
due to pos == last, and then "p->free_raw_bufs = cl->next" in
ngx_event_pipe_read_upstream() dropped both chain links to the buffer
from the p->free_raw_bufs list.

Fix is to move "p->free_raw_bufs = cl->next" before calling the
p->input_filter().

Previously if ngx_add_event() failed a connection was freed two times (once
in the ngx_event_connect_peer(), and again by a caller) as pc->connection was
left set.  Fix is to always use ngx_close_connection() to close connection
properly and set pc->connection to NULL on errors.

Patch by Piotr Sikora.

It's already called by OPENSSL_config().  Calling it again causes some
openssl engines (notably GOST) to corrupt memory, as they don't expect
to be created more than once.

Support for TLSv1.1 and TLSv1.2 protocols was introduced in OpenSSL 1.0.1
(-beta1 was recently released).  This change makes it possible to disable
these protocols and/or enable them without other protocols.

Events from eventfd do not have c->write set, and the stale event
check added in r4306 causes null pointer dereference.

It is currently used from master process on abnormal worker termination to
unlock accept mutex (unlocking of accept mutex was broken in 1.0.2).  It is
expected to be used in the future to unlock other mutexes as well.

Shared mutex code was rewritten to make this possible in a safe way, i.e.
with a check if lock was actually held by the exited process.  We again use
pid to lock mutex, and use separate atomic variable for a count of processes
waiting in sem_wait().