Rename "string" pstrdup argument to "in"

The former name collides with a symbol also used in the isolation test's
parser, causing assorted failures in certain platforms.

src/common/fe_memutils.c

@@ -67,17 +67,17 @@ pg_realloc(void *ptr, size_t size)
  * "Safe" wrapper around strdup().
  */
 char *
-pg_strdup(const char *string)
+pg_strdup(const char *in)
 {
 	char	   *tmp;
 
-	if (!string)
+	if (!in)
 	{
 		fprintf(stderr,
 				_("cannot duplicate null pointer (internal error)\n"));
 		exit(EXIT_FAILURE);
 	}
-	tmp = strdup(string);
+	tmp = strdup(in);
 	if (!tmp)
 	{
 		fprintf(stderr, _("out of memory\n"));
@@ -116,9 +116,9 @@ pfree(void *pointer)
 }
 
 char *
-pstrdup(const char *string)
+pstrdup(const char *in)
 {
-	return pg_strdup(string);
+	return pg_strdup(in);
 }
 
 void *

src/include/common/fe_memutils.h

@@ -9,7 +9,7 @@
 #ifndef FE_MEMUTILS_H
 #define FE_MEMUTILS_H
 
-extern char *pg_strdup(const char *string);
+extern char *pg_strdup(const char *in);
 extern void *pg_malloc(size_t size);
 extern void *pg_malloc0(size_t size);
 extern void *pg_realloc(void *pointer, size_t size);