Intermediate commit.  Filling out new variable handler framework.
Continue refactoring:
+ Switch most access to the Variables class.
+ Redo VariableAccessor to go through the new VariableHandler
+ Move towards handling variables the same way between trans exec and regular bootstrap host
Code cleanup, more on variables capabilities:
- Unify all the variable name constants into a single file, VariableConstants.
- Add a new catalog object, VariableConfig, which will replace GlobalConfig and hold
  variable value metadata, scoping, etc.
- Use the known variable objects where necessary.
- Arrange to initialize variable subsystem on system startup, remove reading of xml files.
- Arrange to find session variable stmt off of new variable subsystem
- Arrange to hook up cache segments with their corresponding variables.
- Arrange for error messages from value metadata classes to be more informative.
- Arrange for nullable/non-nullable variables.
- Generalize the VariableAccessor framework to handle user/session/globals in the same way.

Many tests still do not work, as not all of the variables have been migrated yet.
Also, values for result sets seem to be incorrectly formatted.
More fixes around variable support:
+ Remove default_dynamic_policy, default_time_zone variables, since defaults
  are now handled as the globally scoped dynamic_policy, time_zone values.
+ Clean up variable support in the parser.  In particular, add support for
  @@global.<foo>, @@session.<foo>, @@<foo>, and so on.
+ Modify the escape keyword infrastructure slightly to handle set global transaction isolation,
  set global names, etc.
+ Clean up use of variable scopes in the parser.
+ Track whether a variable reference is lhs or rhs.  If lhs we generally normalize to the
  global <foo> version.
+ Add info schema table variable_definitions for enquiring about metadata of variables.
+ Add info schema tables session_variables and global_variables.
+ Add support for querying variables with where clauses on the show commands and queries
  against the info schema tables.  For all cases other than the simple select <columns>
  from ... where name like ... we find the variable set, create a temp table, load the variable
  values in to the table and execute the query against the temp table.
+ Add an enumeration for mysql transaction isolation values.  Use the enumeration in place of
  various switch statements.
+ Arrange for the LogicalSchemaQueryEngine to execute queries against the variable tables differently.
+ Remove the hardcoded show variables where .... result set.  Add a ton of variables to known variables
  in order to return the same result set.
+ Add an enumeration of sql modes to SQLMode.  Yank functionality from the variable interface into
  SQLMode, and arrange for the SQL_MODE variable handler to store a SQLMode object.
+ Stub out variables appropriately on the NullConnectionContext, also on the TransientExecutionEngine.
+ Arrange for privilege checking when processing set variable statements.
+ Fix some race conditions in the ServerGlobalVariableStore
Many more changes for global variables:

+ Removed the xml variable configuration files for session, global, status variables.
+ Add sql for adding new session/global variables.  For example:

  alter dve add variable cheese options='NULLABLE' scopes='GLOBAL,SESSION' valuetype='varchar' value='cheddar' description='cheese!'

  This replaces the old method of adding an entry to one of the xml files.  Executing this will
  persist information about the variable into the catalog and broadcast a message to all DVE servers such that
  the variables is recognized on all servers, even from a cold cluster start.
+ Removed the GlobalConfig catalog entity.  It has been replaced by VariableConfig.
+ Removed the default_policy_id and default_storage_group from Project.  These are now stored as VariableConfigs.
+ Switched VariableConfig from an integral field denoting emulation to a String field with variable options.
+ Enabled addition of new variables via the OnGlobalConfigChangeMessage.
+ Move variable initialization to catalog creation time.
+ Moved status variables to the current paradigm (one handler per variable).
+ Added an upgrade to migrate config records to varconfig records, also to modify project to remove columns.
+ Added some infrastructure for verifying upgrade catalog state, not just structure.
+ Removed the previous variable infrastructure to avoid confusion.
Fix info schema for Project.
Integrate changes.
mysql -A was hanging because we never flushed the error response for MSPComFieldList.
Change the write call to writeAndFlush, per Sean's suggestion.
Merge branch 'master' into kanzaros_cta

Conflicts:
	tesora-dve-common/src/main/java/com/tesora/dve/common/PEContext.java