Fixed Issue 74 (ERR just returned on invalid password), now the error message is -ERR invalid password.

A trivial change makes the new implementation O(log(N)) instead of O(log(N))+O(M) when there are M repeated scores!

backward support to skiplists for ZREVRANGE, still broken, committing since I've to merge the Solaris patches

initial skiplist implementation. Most memory checks removed and zmalloc() modified to fail with an error message and abort. Anyway Redis is not designed to recover from out of memory conditions.

version incremented to 1.050 to distinguish from 1.001 stable and next stable versions with minor fixes