in 32bit machine, popcount don't work with a input string length up to 512 MB,
bitcount commant may return negtive integer with string length more than 256 MB
use long long instead of size_t make it more safe
Added more info about 32 bit builds into README.
Merge pull request #1093 from july2993/unstable

in 32bit machine, popcount don't work with a input string length up to 5...
Revert "use long long instead of size_t make it more safe"

This reverts commit 2c75f2cf1aa0d9cc8256517bd6f3d8a82088ee1a.

After further analysis, it is very unlikely that we'll raise the
string size limit to > 512MB, and at the same time such big strings
will be used in 32 bit systems.

Better to revert to size_t so that 32 bit processors will not be
forced to use a 64 bit counter in normal operations, that is currently
completely useless.
Test: various issues with the replication-4.tcl test fixed.

The test actually worked, but vars for master and slave were inverted
and sometimes used incorrectly.
Test: check that replication partial sync works if we break the link.

The test checks both successful syncs and unsuccessful ones by changing
the backlog size.
Version bumped to 2.9.10
Test: more PSYNC tests (backlog TTL).
Obtain absoute path of configuration file, expose it in INFO.
CONFIG REWRITE: Initial support code and design.
CONFIG REWRITE: support for save and syslog-facility.
CONFIG REWRITE: support for dir and slaveof.
CONFIG REWRITE: support for client-output-buffer-limit.
CONFIG REWRITE: strip multiple empty lines.
CONFIG REWRITE: remove orphaned lines.
redis-cli: help.h updated.
CONFIG REWRITE: actually rewrite the config file, atomically.
CONFIG REWRITE: Use sane perms when creating redis.conf from scratch.
Added a define for most configuration defaults.

Also the logfile option was modified to always have an explicit value
and to log to stdout when an empty string is used as log file.

Previously there was special handling of the string "stdout" that set
the logfile to NULL, this always required some special handling.