Merge pull request #1301 from henryzhao81/master

Reduce risk for infinite loop
Update README.md
Fixed issue 1302 about ordering of properties in schema
Merge branch 'master' of https://github.com/nuvolabase/orientdb
SQL: fixed bug on AVG function against group by
Fixed issue #1293 adding server.dblist resource to the guest user
Merge pull request #1305 from henryzhao81/master

Always Lost one record when shutdown remote server in distributed mode issue <https://github.com/nuvolabase/orientdb/issues/1304>
Fixed issue #1292
Merge branch 'master' of https://github.com/nuvolabase/orientdb
Fixed eval() function by returning always 0 in case of arithmetic exception
FIxed issue #1310
Extendible hashing was partially implemented.
Json: fixed map management
Merge branch 'master' of https://github.com/nuvolabase/orientdb
Calculation of end position of cluster was fixed.
Added embedded checks when building the ridMap
Merge pull request #1314 from adaher/master_RIDMAP_EMBCHECKS

Added embedded checks when building the ridMap
1. Extendible hashing was implemented.
2. Linear hashing was replaced in favor of extendible hashing to make non-uniform key distribution processing faster.
Fixed issue #1027

Since I've not a test case I've added more checks about Nullity. Hope
it's enough!
Merge branch 'master' of https://github.com/nuvolabase/orientdb