For some reason, Mac client is the only project that references
libtransmission files as if they were a part of its own project, and
inconsistently so. Make the include/import style uniform an in line with
other projects.
Adjust Mac client include directory settings a bit along the way.
This makes the variable naming more uniform. It also clarifies the information we're really trying to convey -- previously, isSingleFile was false whenever the torrent held a directory tree, even if there was only a single file in the tree.
Sync the Mac OS X client's use to match the libtransmission variable names.
