Fix comparisons of pointers with zero to compare with NULL instead.

Per C standard, these are semantically the same thing; but saying NULL
when you mean NULL is good for readability.

Marti Raudsepp, per results of INRIA's Coccinelle.

src/backend/regex/regc_lex.c

@@ -846,7 +846,7 @@ lexescape(struct vars * v)
 			if (ISERR())
 				FAILW(REG_EESCAPE);
 			/* ugly heuristic (first test is "exactly 1 digit?") */
-			if (v->now - save == 0 || ((int) c > 0 && (int) c <= v->nsubexp))
+			if (v->now == save || ((int) c > 0 && (int) c <= v->nsubexp))
 			{
 				NOTE(REG_UBACKREF);
 				RETV(BACKREF, (chr) c);

src/backend/utils/adt/tsrank.c

@@ -395,7 +395,7 @@ getWeights(ArrayType *win)
 	int			i;
 	float4	   *arrdata;
 
-	if (win == 0)
+	if (win == NULL)
 		return weights;
 
 	if (ARR_NDIM(win) != 1)

src/backend/utils/fmgr/dfmgr.c

@@ -616,7 +616,7 @@ find_in_dynamic_libpath(const char *basename)
 					(errcode(ERRCODE_INVALID_NAME),
 					 errmsg("zero-length component in parameter \"dynamic_library_path\"")));
 
-		if (piece == 0)
+		if (piece == NULL)
 			len = strlen(p);
 		else
 			len = piece - p;

src/bin/pg_dump/pg_backup_tar.c

@@ -576,7 +576,7 @@ tarWrite(const void *buf, size_t len, TAR_MEMBER *th)
 {
 	size_t		res;
 
-	if (th->zFH != 0)
+	if (th->zFH != NULL)
 		res = GZWRITE((void *) buf, 1, len, th->zFH);
 	else
 		res = fwrite(buf, 1, len, th->nFH);

src/port/dirmod.c

@@ -246,7 +246,7 @@ pgsymlink(const char *oldpath, const char *newpath)
 	else
 		strcpy(nativeTarget, oldpath);
 
-	while ((p = strchr(p, '/')) != 0)
+	while ((p = strchr(p, '/')) != NULL)
 		*p++ = '\\';
 
 	len = strlen(nativeTarget) * sizeof(WCHAR);

src/timezone/zic.c

@@ -810,7 +810,7 @@ associate(void)
 			 * Note, though, that if there's no rule, a '%s' in the format is
 			 * a bad thing.
 			 */
-			if (strchr(zp->z_format, '%') != 0)
+			if (strchr(zp->z_format, '%') != NULL)
 				error(_("%s in ruleless zone"));
 		}
 	}
@@ -1111,9 +1111,9 @@ inzsub(char **fields, int nfields, int iscont)
 	z.z_filename = filename;
 	z.z_linenum = linenum;
 	z.z_gmtoff = gethms(fields[i_gmtoff], _("invalid UTC offset"), TRUE);
-	if ((cp = strchr(fields[i_format], '%')) != 0)
+	if ((cp = strchr(fields[i_format], '%')) != NULL)
 	{
-		if (*++cp != 's' || strchr(cp, '%') != 0)
+		if (*++cp != 's' || strchr(cp, '%') != NULL)
 		{
 			error(_("invalid abbreviation format"));
 			return FALSE;
@@ -1438,9 +1438,9 @@ rulesub(struct rule * rp, const char *loyearp, const char *hiyearp,
 	}
 	else
 	{
-		if ((ep = strchr(dp, '<')) != 0)
+		if ((ep = strchr(dp, '<')) != NULL)
 			rp->r_dycode = DC_DOWLEQ;
-		else if ((ep = strchr(dp, '>')) != 0)
+		else if ((ep = strchr(dp, '>')) != NULL)
 			rp->r_dycode = DC_DOWGEQ;
 		else
 		{
@@ -2826,7 +2826,7 @@ mkdirs(char *argname)
 	if (argname == NULL || *argname == '\0')
 		return 0;
 	cp = name = ecpyalloc(argname);
-	while ((cp = strchr(cp + 1, '/')) != 0)
+	while ((cp = strchr(cp + 1, '/')) != NULL)
 	{
 		*cp = '\0';
 #ifdef WIN32