shared memory code 'memalooc.c' has 2 critical bugs.

1) It does not confirm enough space to split free chunk.
There are 3 points to split free chunk area to 1 free and 1 used. But a point does not confirm enough space. So, it has a possiblity to produce the gabage which size is lesser than MEM_MIN_ALLOC and occur memory corruption! At least, I found the decreasing of free_size for configuration cache in spite of unchanging configuration.

2) It has a calculation mistake for free chunk area after integration, which is not so critical. But free_size is continously decreasing.

So, I attached fixed patch.