pgwin32_is_junction's argument should be "const char *" not "char *".

We're passing const strings to it in places, and that's not an
unreasonable thing to do.  Per buildfarm (noted on frogmouth
in particular).

src/include/port.h

@@ -251,7 +251,7 @@ extern int	pgunlink(const char *path);
 #if defined(WIN32) && !defined(__CYGWIN__)
 extern int	pgsymlink(const char *oldpath, const char *newpath);
 extern int	pgreadlink(const char *path, char *buf, size_t size);
-extern bool pgwin32_is_junction(char *path);
+extern bool pgwin32_is_junction(const char *path);
 
 #define symlink(oldpath, newpath)	pgsymlink(oldpath, newpath)
 #define readlink(path, buf, size)	pgreadlink(path, buf, size)

src/port/dirmod.c

@@ -338,10 +338,10 @@ pgreadlink(const char *path, char *buf, size_t size)
 
 /*
  * Assumes the file exists, so will return false if it doesn't
- * (since a nonexistant file is not a junction)
+ * (since a nonexistent file is not a junction)
  */
 bool
-pgwin32_is_junction(char *path)
+pgwin32_is_junction(const char *path)
 {
 	DWORD		attr = GetFileAttributes(path);