Rename the internal structures of the CREATE TABLE (LIKE ...) facility

The original implementation of this interpreted it as a kind of
"inheritance" facility and named all the internal structures
accordingly.  This turned out to be very confusing, because it has
nothing to do with the INHERITS feature.  So rename all the internal
parser infrastructure, update the comments, adjust the error messages,
and split up the regression tests.

src/include/nodes/parsenodes.h

@@ -504,16 +504,16 @@ typedef struct ColumnDef
 } ColumnDef;
 
 /*
- * inhRelation - Relation a CREATE TABLE is to inherit attributes of
+ * TableLikeClause - CREATE TABLE ( ... LIKE ... ) clause
  */
-typedef struct InhRelation
+typedef struct TableLikeClause
 {
 	NodeTag		type;
 	RangeVar   *relation;
-	bits32		options;		/* OR of CreateStmtLikeOption flags */
-} InhRelation;
+	bits32		options;		/* OR of TableLikeOption flags */
+} TableLikeClause;
 
-typedef enum CreateStmtLikeOption
+typedef enum TableLikeOption
 {
 	CREATE_TABLE_LIKE_DEFAULTS = 1 << 0,
 	CREATE_TABLE_LIKE_CONSTRAINTS = 1 << 1,
@@ -521,7 +521,7 @@ typedef enum CreateStmtLikeOption
 	CREATE_TABLE_LIKE_STORAGE = 1 << 3,
 	CREATE_TABLE_LIKE_COMMENTS = 1 << 4,
 	CREATE_TABLE_LIKE_ALL = 0x7FFFFFFF
-} CreateStmtLikeOption;
+} TableLikeOption;
 
 /*
  * IndexElem - index parameters (used in CREATE INDEX)