Fix typos in comments

Author: Peter Smith <smithpb2250@gmail.com>
Discussion: https://postgr.es/m/CAHut+PsN_gmKu-KfeEb9NDARoTPbs4AN4PPu=6LZXFZRJ13SEw@mail.gmail.com

src/backend/access/transam/xlogreader.c

@@ -231,7 +231,7 @@ WALOpenSegmentInit(WALOpenSegment *seg, WALSegmentContext *segcxt,
 /*
  * Begin reading WAL at 'RecPtr'.
  *
- * 'RecPtr' should point to the beginnning of a valid WAL record.  Pointing at
+ * 'RecPtr' should point to the beginning of a valid WAL record.  Pointing at
  * the beginning of a page is also OK, if there is a new record right after
  * the page header, i.e. not a continuation.
  *

src/backend/commands/copyfrom.c

@@ -1237,7 +1237,7 @@ BeginCopyFrom(ParseState *pstate,
 
 	tupDesc = RelationGetDescr(cstate->rel);
 
-	/* process commmon options or initialization */
+	/* process common options or initialization */
 
 	/* Generate or convert list of attributes to process */
 	cstate->attnumlist = CopyGetAttnums(tupDesc, cstate->rel, attnamelist);