[RFA]: Race safe fwalk

[Thomas Pfaff <tpfaff at gmx dot net>]

There is a possible race between fwalk and fopen:

When a thread make a call to fopen the FILE * _flags will be set to 1 in 
findfp to mark it used and later it will be changed to the real FILE flag.

When another thread calls fwalk during that time fwalk will treat the 
FILE as already opened and calls the callback functions with the yet 
unopened and only partially initialized FILE *.

This can be avoided by checking for fp->_flags != 0 && fp->_flags != 1. 
Since _flags is signed short i did not check for _flags > 1. The flag 
should be set as the last step in an open call.
I do not think that 1 is a valid _flag for an open file. Correct me if 
am wrong.

2004-03-08  Thomas Pfaff  <tpfaff@gmx.net>

	* libc/stdio/fdopen.c (_fdopen_r): Add missing
	__lock_init_recursive.
	Set FILE flags as the last step.
	* libc/stdio/fopen.c (_fopen_r): Set FILE flags as the last
	step.
	* libc/stdio/fwalk.c: Check for _flags != 1 to make sure that
	file is really open.
	* libc/stdio64/fdopen64.c (_fdopen64_r): Set FILE flags as the
	last step.
	* libc/stdio64/fopen64.c (_fopen64_r): Ditto.