TRANSACTION CACHE SIZE IS EXACTLY 32768

Problem:
========
When the binlog's IO_CACHE grows up to exact 32768 bytes it
causes binlog events to get corrupt, if this transaction
precedes with a transaction whose IO_CACHE size is >32768.

Analysis:
========
On the master during the execution of a transaction all the
events that are related to that transaction will be written
to the IO_CACHE. The size of the IO_CACHE is 32768.

The transaction whose events can fit within the IO_CACHE
are never flushed to disk. During flush operation they do
nothing but simply set the cache->read_end and end_of_file
to current size. At the time of writing to the binlog the
cache is read back and if CRC is enabled checksum is
calculated if not then the content is written to binlog file.

If the transaction size exceeds 32768 then it will be
written to a temporary file and the cache is reinited so
that remaining events can be written to cache. During
writing to binary log file this temp file is read back.

In the bug scenario the transaction size grows exactly to
32768, and during flush operation it expects current size of
cache to be < 32768. Which is incorrect ideally it should
have been <= 32768. As the size is still equal to IO_CACHE
size.

Because of the incorrect check cache is marked for flush but
the writing function "my_b_write" doesn't flush the buffer
to disk as it expects cache size to be > 32768 and the cache
is reinited without writing to temp file. When the cache is
read back it finds the buffer to be empty and tries to fill
it from temp file which wrong. Hence the buffer is filled
with some other transaction related data causing corruption.


Fix:
===
During flush the check for size has been changed from "<" to
"<=".