rename packet sampling macro to PKT_SAMPLING
ALWAYS release ThreadPool before PollMgr

some running task might want to access PollMgr (update_mode),
causing SIGSEGV
added ordered rpc attribute and demo code
forbid using reserved __NAME__ names in rpc definition
Revert "added ordered rpc attribute and demo code"

Give up ordered-rpc branch. Proxy classes are supposed to be
small and copyable. Adding sequence counter into it will make
it no longer copyable. Also, queueing need to base on client
address. When using multiple parallel connections, order can
no longer be preserved.

This reverts commit e27be4e37b9ca31bee3b2c9fd310b0cb9576a394.

Conflicts:
	rpc/rpcgen.g
	rpc/rpcgen.py
	test/demo_service.h
	test/demo_service.rpc
proper file mode for rpcgen.g
Merge branch 'master' of github.com:santazhang/simple-rpc