Lua debugger: support direct calls to SCRIPT DEBUG in redis-cli.
Lua debugger: support direct calls to SCRIPT DEBUG in redis-cli.

Previously it was possible to activate a debugging session only using
the --ldb option in redis-cli. Now calling SCRIPT DEBUG can also
activate the debugging mode without putting the redis-cli in a
desynchronized state.

Related to #2952.

pedigree/redis,janekmi/redis,xuguruogu/redis,pedigree/redis,4396/redis,xuguruogu/redis,xuguruogu/redis,4396/redis,pedigree/redis,4396/redis,janekmi/redis,xuguruogu/redis,4396/redis,janekmi/redis,pedigree/redis,janekmi/redis