use bio.c instead of libeio for closing the AOF file in background. Some comment added and other minor changes.

Remove the write handler only if there are no longer objects in the output queue AND if the static buffer is empty. This bug was the cause of a possible server-stop-responding-to-client bug under some specific work load. Thanks to Pieter Noordhuis for spotting and fixing it.

Auto rewrite integer overflow fixed. Thanks to Gaurav for finding it (see issue 602 on google code), and Pieter Noordhuis for tracing it.

prepareForShutdown() fixed for correctness regarding what to do with AOF and RDB persistence on exit.

Added a 'runtest' script that is responsible to check if Tcl is available and run the test. This is invoked from Makefile as well.

top level Makefile now just a proxy. Doing make clean inside src now does a full clean including deps, not just Redis source. Thanks to Pieter for the top level Makefile proxy trick.