Fixed a config docs typo.

AOF fileds in the global server state, and define names, renamed with more consistent names. More work to do.

server.appendonly -> server.aof_state, and many comments added in the server global state structure in the process.

Redis test: when assertion fails print not just the expression but also expanded values in the error message.

Fix issue #247 and add a test case

Added a naive unit test for SORT-LIMIT command.

Using `getLongFromObjectOrReply` instead of `atoi` if possible.
The following functions are modified.

* lrangeCommand
* ltrimCommand
* lremCommand
* lindexCommand
* lsetCommand
* zunionInterGenericCommand
* genericZrangebyscoreCommand
* sortCommand

Fixed memleak in CLIENT INFO, added simple test that will work as regression test on mac os x and in the CI when running over valgrind. This fixes issue #256

loop is never destroyed in Redis). Thanks to @anydot for noticing it.

Fix: when aof_write_rewrite is true don't append on the AOF buffer but accumulate the differences for the rewrite.

AOF fixes in the context of replicaiton (when AOF is used by slave) and CONFIG SET appendonly yes/no.