Remove a bunch more of types2.
A new exception class for this subsystem.
Still keeping AkType, but in a higher directory.
A little more removed.
types3 -> types.
t3expressions -> expressions.
merge MMcM: More Types2 removal

Merge pull request #957 from MMcM/akiban-server/less-types2
https://github.com/FoundationDB/sql-layer/pull/957
Remaining t3's in names.
It missed these resources. I must not have the IDE configured right.
merge MMcM: Rename types3

Merge pull request #958 from MMcM/akiban-server/rename-types3
https://github.com/FoundationDB/sql-layer/pull/958