Error message was 'too few arguments for "find"' because the "base"
constraint was not supported, and no other constraints remained.

Checking "!open" did not work with the NFS plugin because that plugin
does not close the file automatically, unlike CURL.

This reverts commit 966c4244.

The commit was bad, because the bug was really in
NfsInputStream::DoRead(); see previous commit.

Avoids off-by-one bug and obsoletes the bug fix in commit 966c4244

Fixes potential crash.

std::map::emplace() is only available from gcc 4.8 on.

More robust and cancellable.

May cause assertion failure.

Check for 0 in "device" and "inode" instead.

Remove the C list_head library and use type-safe C++ instead.

See https://svn.boost.org/trac/boost/ticket/7849

Eliminate extra allocations for the std::list node instances.

Make valgrind happy.

Make valgrind happy.