Use built-in __APPLE__ macro instead of SYS_DARWIN and MACOSX

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14310 f4695dd4-2c0a-0410-b89c-da849a56a58e
(trunk, libT) #5709 'Fix an instance of time_t printing' -- fixed, patch by naddy

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14311 f4695dd4-2c0a-0410-b89c-da849a56a58e
(trunk, libT) #5699 'Toggle Inspector's Origin: is incorrect' -- fixed, patch by enzotrew

git-svn-id: svn://svn.transmissionbt.com/Transmission/trunk@14312 f4695dd4-2c0a-0410-b89c-da849a56a58e