Weeks ago trying to fix an harmless GCC warning I introduced a bug in
the ziplist-encoded implementations of sorted sets.

The bug completely broke zuiNext() iterator, that is used in the
ZINTERSTORE and ZUNIONSTORE implementation, so those two commands are no
longer reliable starting from Redis version 2.4.12 and latest 2.6.0-RC
releases.

This commit fixes the problem and adds a regression test.

string to number API is now more strict not accepting spaces before or after the number. A few tests converted to match the new error messages using the word float instead of double.

This also optimizes ZREVRANGEBYSCORE for pathological cases where a
sorted set contains many elements with the same score. Previously,
it would traverse the list from back to front in such a case.

This allows to use inclusive/exclusive bounds for min and max when
deleting a range of scores from a sorted set.

Return an error when the resulting value is not a number (NaN). Fix
ZUNIONSTORE/ZINTERSTORE to clean up when a weight argument is not a
double value.

When +inf and -inf are added, the result is NaN. We don't want NaN
scores in a sorted set, so agreed on the result of this operation being
zero.

changed how server.tcl accepts options to support more directives without requiring more arguments to the proc