Fix typos in comments

Fix various typos that seemed common.

src/backend/cdb/cdbpersistentfilesysobj.c

@@ -4731,7 +4731,7 @@ static void PersistentFileSysObj_ScanStateAction(
 				WRITE_PERSISTENT_STATE_ORDERED_LOCK;
 				/*
 				 * We calculate only RelationFile objects to create for resync.
-				 * As it seems unneccessary overhead to scan database/tablespace/etc..
+				 * As it seems unnecessary overhead to scan database/tablespace/etc..
 				 * Hence only decrement for RelationFile.
 				 */
 				if (fsObjType == PersistentFsObjType_RelationFile)
@@ -4909,7 +4909,7 @@ static void PersistentFileSysObj_ScanStateAction(
 
 					/*
 					 * We calculate only RelationFile objects to create for resync.
-					 * As it seems unneccessary overhead to scan database/tablespace/etc..
+					 * As it seems unnecessary overhead to scan database/tablespace/etc..
 					 * Hence only decrement for RelationFile.
 					 */
 					if (fsObjType == PersistentFsObjType_RelationFile)

src/backend/executor/nodeAgg.c

@@ -1069,7 +1069,7 @@ ExecAgg(AggState *node)
 					}
 					node->hhashtable->state = HASHAGG_END_OF_PASSES;
 					/*
-					 * pass through. Be sure that the next case statment
+					 * pass through. Be sure that the next case statement
 					 * is HASHAGG_END_OF_PASSES.
 					 */
 

src/backend/gpopt/translate/CTranslatorDXLToScalar.cpp

@@ -168,8 +168,8 @@ CTranslatorDXLToScalar::PcaseexprFromDXLNodeScIfStmt
 	CDXLNode *pdxlnCurr = const_cast<CDXLNode*>(pdxlnIfStmt);
 	Expr *pexprElse = NULL;
 
-	// An If statment is of the format: IF <condition> <then> <else>
-	// The leaf else statment is the def result of the case statement
+	// An If statement is of the format: IF <condition> <then> <else>
+	// The leaf else statement is the def result of the case statement
 	BOOL fLeafElseStatement = false;
 
 	while (!fLeafElseStatement)