Added simple wrappers for fopen(3) and fclose(3).

Add simple wrapper functions for fopen(3) and fclose(3) that are
somewhat akin to the nxt_file_open() and nxt_file_close() wrappers that
log errors.

Suggested-by: Alejandro Colomar <alx@nginx.com>
Reviewed-by: Alejandro Colomar <alx@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

src/nxt_file.h

@@ -186,6 +186,10 @@ NXT_EXPORT ssize_t nxt_fd_write(nxt_fd_t fd, u_char *buf, size_t size);
 NXT_EXPORT ssize_t nxt_fd_read(nxt_fd_t fd, u_char *buf, size_t size);
 NXT_EXPORT void nxt_fd_close(nxt_fd_t fd);
 
+NXT_EXPORT FILE *nxt_file_fopen(nxt_task_t *task, const char *pathname,
+    const char *mode);
+NXT_EXPORT void nxt_file_fclose(nxt_task_t *task, FILE *fp);
+
 NXT_EXPORT nxt_int_t nxt_file_redirect(nxt_file_t *file, nxt_fd_t fd);
 NXT_EXPORT nxt_int_t nxt_file_stderr(nxt_file_t *file);
 NXT_EXPORT nxt_int_t nxt_stderr_start(void);