GSFileHandle and GNUMail

[Enrico Sersale]

After the last change in GSFileHandle (Fix reversed logic of non-blocking I/O 
in -availableData), GNUMail crashes while getting mail from the server with:

"NSFileHandleOperationException: unable to read from descriptor - Resource 
temporarily unavailable"

reverting to the old version of -availableData fixes the problem.
I don't know if this can help but also simply not raising the exception in case of 
"Resource temporarily unavailable" makes GNUMail to work.

Here is the stack (even if it doesn't say anything besides the fact that the 
exception has raised)

#0  0x0030a402 in __kernel_vsyscall ()
#1  0x00a601f8 in raise () from /lib/libc.so.6
#2  0x00a61948 in abort () from /lib/libc.so.6
#3  0x00394e25 in _NSAppKitUncaughtExceptionHandler (exception=0x93d4da0)
    at NSApplication.m:140
#4  0x0078ce19 in -[NSException raise] (self=0x93d4da0, _cmd=0x980af8)
    at NSException.m:173
#5  0x007ebdf6 in -[NSRunLoop acceptInputForMode:beforeDate:] (self=0x90c7870,
    _cmd=0x980b60, mode=0x980be0, limit_date=0x917c5c8) at NSRunLoop.m:1084
#6  0x007ec09f in -[NSRunLoop runMode:beforeDate:] (self=0x90c7870,
    _cmd=0x60f518, mode=0x980be0, date=0x90ccc50) at NSRunLoop.m:1134
#7  0x00506ffb in -[GSDisplayServer(EventOps) 
getEventMatchingMask:beforeDate:inMode:dequeue:] (self=0x909b998, 
_cmd=0x102eb40, mask=4294967295,
    limit=0x90ccc50, mode=0x980be0, flag=1 '\001') at GSDisplayServer.m:868
#8  0x00fd45cd in -[XGServer(X11Ops) 
getEventMatchingMask:beforeDate:inMode:dequeue:] (self=0x909b998, 
_cmd=0x586738, mask=4294967295, limit=0x90ccc50,
    mode=0x980be0, flag=1 '\001') at XGServerEvent.m:1975
#9  0x0039ab00 in DPSGetEvent (ctxt=0x909b998, mask=4294967295,
    limit=0x90ccc50, mode=0x980be0)
    at ../Headers/Additions/GNUstepGUI/GSDisplayServer.h:177
#10 0x0039b40c in -[NSApplication 
nextEventMatchingMask:untilDate:inMode:dequeue:] (self=0x90d4f68, 
_cmd=0x586988, mask=4294967295, expiration=0x90ccc50,
    mode=0x980be0, flag=1 '\001') at NSApplication.m:1918
#11 0x00399b5e in -[NSApplication run] (self=0x90d4f68, _cmd=0x57f668)
    at NSApplication.m:1358
#12 0x003892b1 in NSApplicationMain (argc=1, argv=0xbf990844) at Functions.m:72
#13 0x0809db3c in main (argc=1, argv=0xbf990844, env=0xbf99084c)
    at GNUMail_main.m:42