don't call synchronizeFile if output goes to socket

There are situations where stdout might be a socket and sockets don't support synchronizeFile. For example if you have the following nodejs script
````JS
var sys = require('sys')
var exec = require('child_process').exec;
function puts(error, stdout, stderr) { sys.puts(stdout); sys.puts(stderr) }
exec("xctool.sh -workspace ... -scheme ... ...", puts);
````

You will get the following error:
````
** BUILD SUCCEEDED ** (3868 ms)

2013-06-13 21:48:54.416 xctool[33910:707] *** Terminating app due to uncaught exception 'NSFileHandleOperationException', reason: '*** -[NSConcreteFileHandle synchronizeFile]: Operation not supported'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff9378db06 __exceptionPreprocess + 198
	1   libobjc.A.dylib                     0x00007fff8db163f0 objc_exception_throw + 43
	2   CoreFoundation                      0x00007fff9378d8dc +[NSException raise:format:] + 204
	3   xctool                              0x00000001046e4b1c -[Reporter close] + 273
	4   xctool                              0x00000001046e5973 -[TextReporter close] + 67
	5   CoreFoundation                      0x00007fff93789460 -[NSArray makeObjectsPerformSelector:] + 272
	6   xctool                              0x00000001046dfd70 -[XCTool run] + 2471
	7   xctool                              0x00000001046dede0 main + 244
	8   xctool                              0x00000001046dece4 start + 52
)
libc++abi.dylib: terminate called throwing an exception
/Users/frankfa/git/xctool//xctool.sh: line 54: 33910 Abort trap: 6           "$XCTOOL_DIR"/build/$REVISION/Products/Release/xctool "$@"
````

I have filed a corresponding issue against nodejs, where you can find more details:
https://github.com/joyent/node/issues/5689

I am forced to run xctool.sh from within nodejs (please don't ask why), so I hope this can be fixed upstream.