Description:
------------
Trying to overwrite a file using ftp without enabling 
the "overwrite" context directive doesn't provide a 
helpful error message.

Line 460 of ext/standard/ftp_fopen_wrapper.c does:

  errno = EEXIST;
  goto errexit;

However, this error number doesn't get translated into 
something accessible. (That I can tell. Am I missing 
something?)

This patch adds a short error message, but I'm not sure 
if this is fixing a symptom instead of a root cause.

http://www.trachtenberg.com/patches/
ftp_overwrite_warning.txt

Reproduce code:
---------------
fopen('ftp://localhost/path/to/existing/file.txt', 'w');

or

file_put_contents('ftp://localhost/path/to/existing/file.txt', 'blah');

Expected result:
----------------
A useful warning message, like:

PHP Warning:  fopen(ftp://...@localhost/path/to/
existing/file.txt): failed to open stream: Cannot 
overwrite file in current mode
FTP server reports 213 17

Actual result:
--------------
General stream failure message, with no description:

PHP Warning:  fopen(ftp://...@localhost/path/to/
existing/file.txt): failed to open stream: FTP server 
reports 213 17