Remove redundant call to worldMaps.a(). Addresses BUKKIT-4828

The WorldMapCollection object for SecondaryWorldServers(Nether, End) is
shared with the main world, so saving it again for each SecondaryWorldServer
is redundant.

This commit removes the redundant call by checking if the WorldServer is an
instanceof SecondaryWorldServer before invoking worldMaps.a().
Re-enable built in auto-save. Fixes BUKKIT-4800

When Minecraft first introduced an auto-save feature, we
were taken by surprise by how much of an impact it actually had on the performance
of the server. After investigating the potential causes of the significant
slow-downs we saw at the time, we came to the conclusion that it was a
combination of the auto-save interval being incredibly frequent and
servers already having an auto-save solution that was conflicting with the
newly added built-in one.

Since we noticed that most servers already had their own auto-save
solution, we decided to completely disable the built in auto-save by
default. In hindsight, however, we were so happy that we discovered and
squashed the cause of the performance issues that we forgot to consider
the future and, as a result, some servers have unfortunately been caught
by surprise when they ran their servers without any auto-save plugins.

Without the auto-save plugin conflict, however, Minecraft's default save
interval of 45 seconds is not suitable for the types of servers that run
Bukkit, to the point where it was negatively impacting performance. As
such, we've decided to re-enable the built in auto-save at an interval of
5 minutes for newly created servers.
Add auto-save plugin redundancy detection.

This change will print a warning when a plugin induces a forced save. A
player or console forcing a save (via a command) is ignored for purposes
of printing a warning.
Updated version to 1.6.4-R1.0 in pom.xml for RB.
Updated version to 1.6.4-R1.1-SNAPSHOT for development towards next release.
Fix our versioning system.
Don't share WorldMapCollection. Fixes BUKKIT-4871

WorldMapCollection stores scoreboard, map (item), structure, and
village information. Scoreboards are explicitly handled globally,
while villages and structures are erroneously shared.

This commit separates the WorldMapCollections to not be shared among
custom worlds. Maps are special-cased to maintain the previous shared
behavior.