Fix for possibility of keyword sharing in language syntax

* ISQLConstants
 * Can be used for SQL syntax and upper-case is the expected norm. Thus,
   the NULL keyword should be held in upper-case

* ISQLStringVisitor
 * Has no need to extend ISQLConstants since its implementations have
   access to their own syntax interfaces

* Synced with change in runtime-clients

plugins/org.teiid.designer.spi/src/org/teiid/designer/query/sql/ISQLConstants.java

@@ -57,6 +57,7 @@ public interface ISQLConstants {
     String TABLE = "TABLE"; //$NON-NLS-1$
     String EXEC = "EXEC"; //$NON-NLS-1$
     String CONVERT = "CONVERT"; //$NON-NLS-1$
+    String NULL = "NULL"; //$NON-NLS-1$
 
     String ENVELOPE_NS = "http://schemas.xmlsoap.org/soap/envelope/"; //$NON-NLS-1$
     String ENVELOPE_NS_ALIAS = "soap"; //$NON-NLS-1$
@@ -96,8 +97,5 @@ public interface ISQLConstants {
     String HEADER = "HEADER"; //$NON-NLS-1$
     String SKIP = "SKIP"; //$NON-NLS-1$
     String WIDTH = "width"; //$NON-NLS-1$
-
-    String NULL = "null"; //$NON-NLS-1$
-
-
+
 }

plugins/org.teiid.designer.spi/src/org/teiid/designer/query/sql/ISQLStringVisitor.java

@@ -12,7 +12,7 @@
 /**
  *
  */
-public interface ISQLStringVisitor<LO extends ILanguageObject> extends ILanguageVisitor, ISQLConstants {
+public interface ISQLStringVisitor<LO extends ILanguageObject> extends ILanguageVisitor {
 
     /**
      * Should the visitor fail to evaluate then this