the file object is not thread safe. with sync I/O just use a single thread in the thread pool for now
the file object is not thread safe. with sync I/O just use a single thread in the thread pool for now

git-svn-id: 51f496e7cf1b55ee487494d18ee2d308bae7fe77@6867 f43f7eb3-cfe1-5f9d-1b5f-e45aa6702bda

steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent,steeve/libtorrent