keep vio from being freed twice when we are low on memory
mysys/safemalloc.c
    changes for --safemalloc-mem-limit
sql/mini_client.cc
    keep vio from being freed twice
sql/mysqld.cc
    changes for --safemalloc-mem-limit
sql/slave.cc
    prevent closing connection twice
sql/sql_string.h
    shrink() did not work right when my_realloc() failed