add flushable switch in config file.

if flushable is 'yes', redis can b flushed. else just return err to
client and do nothing.
add cscope database and ctags index file to .gitignore
add flushable yes to default.conf for "make test
record remote ip and port in redisClient struct.
add accesslog switch, and if it is true, log will record accesslog.
edit config.c make the flushable and accesslog switch can be set/unset
without redis rebooting.
add config Command's whitelist ip.
add access whitelist function
move filter to accept handler
move dicttype position
add traceadd tracedel traceshow command
add tracekeys commond and fix make test problem
add tracestates config
Merge pull request #1 from gaoxiaogp/didi2.8.12

add access whitelist function
fix the tiny bug.
Merge pull request #2 from hurricane1026/hotfix_didi2.8.12_rewrite

fix the tiny bug.
add trace test
Merge remote branch 'upstream/didi2.8.12' into didi2.8.12
merge 2.8.13
Merge pull request #3 from gaoxiaogp/didi2.8.13

Didi2.8.13