doc-view works with remote files, compressed files and files inside archives now

[Tassilo Horn]

Hi all,

my latest changes to doc-view enable it to work with remote files,
compressed files and files inside archives.  If you open such a file a
(uncompressed, extracted, local) copy is put into your
doc-view-cache-directory which will be used for conversion (and
md5-summing to find its cached images).

When toggling from images to text and back again with C-c C-c all
modifications of the text will cause a new conversion and the changes
will be propagated back to the remote host, the compressed file or
original file in the archive.  Thus there should be no difference to
plain, local PDF/PS/DVI files.

I've tested it with some local files, files inside a local foo.tar.gz
archive, local compressed files (foo.ps.gz), remote files accessed with
TRAMP and remote compressed files (again TRAMP).

I don't use any TRAMP specific code anymore, so I guess it should work
the same with ange-ftp.

Happy doc-viewing,
Tassilo