occurs when two or more dbs are replicated and at least one of them is >db10

Fix for slaves chains. Force resync of slaves (simply disconnecting them)  when SLAVEOF turns a master into a slave.

(The original implementation was modified by @antirez to conform Redis
coding standards.)

Redis test: regexp to check if valgrind reported errors modified. Now we no longer look at the total count because this includes "possibly lost" bytes that are not interesting for Redis (tons of false positives because of how sds.c works).

Produce the watchlog warning log in a way that is safer from a signal handler. Fix a memory leak in the backtrace generation function.

This is required to ensure that the signal will be delivered to the main
thread when the watchdog timer expires.

SIGSEGV handler refactored so that we can reuse stack trace and current client logging functionalities in other contexts.

This new field counts all the times Redis is configured with AOF enabled and
fsync policy 'everysec', but the previous fsync performed by the
background thread was not able to complete within two seconds, forcing
Redis to perform a write against the AOF file while the fsync is still
in progress (likely a blocking operation).

Apparently because the sample RDB file was not copied before every test
Redis had a chance to replace it with a newly written one, so that the
next test could fail.

When running the test in valgrind mode, pass the right flags to show memory leaks stack traces but only including the "definitely lost" items.

Result of INCRBYFLOAT and HINCRBYFLOAT should never be in exponential form, and also should never contain trailing zeroes. This is not possible with vanilla printf() format specifiers, so we alter the output.

DEBUG should not be flagged as w otherwise we can not call DEBUG DIGEST and other commands against read only slaves.