[syslinux] Problem with NTFS support

[Shao Miller]

So in NTFS, the Master File Table is itself a file.  That means it can have
extents.  An easy way to process its records is thus to read it as a file
using functions in core/fs/fs.c.

However, the functions in core/fs/fs.c mostly assume the "global," Syslinux,
booted-from filesystem ('this_fs').  The Syslinux filesystem drivers try to
tie all data to a particular FS instance.

So if an FS driver wants to open a file, it probably wants to do it _from_ a
particular FS instance, such as opening the MFT.

Anyway, please see commit bcb5af34d4fd02c5bd2970c89d30275cd9176168[1] and
please advise how this could be done better.  For example, what are the
interfaces going to be like in the future, when code can specify a desired
filesystem to open a file on?

- Shao Miller

[1]
http://git.zytor.com/?p=users/sha0/syslinux.git;a=commitdiff;h=bcb5af34d4fd0
2c5bd2970c89d30275cd9176168