Add fallback for (file-)systems without mmap

[anonymous]

Not all systems or filesystems support mmap, others do but not in a stable manner. Examples include FUSE mounted filesystems such as sshfs, encfs and ntfs, or nfs in older Linux kernels. (See for example ticket #226 and #322.) Hence, it would be nice if libtorrent could, as a user preference, fallback to using ordinary read/write.

This would obviously be a performance hit, but a little slower is better than not working at all.

Google found the following, which perhaps can be of use in a future implementation:  http://lists.debian.org/deity/2005/06/msg00134.html

Adding to 1.1 since 0.9 should focus on the client and 1.0 on stability and fine-adjustments, not because it wouldn't be nice to have it earlier.

[rakshasa]

This would depend on #641 being implemented.

[anonymous]

FUSE supports shared writable mmap since Linux kernel 2.6.26, so upgrade to a newer kernel.