Support local filesystem quirks

[Facundo Batista]

The client should support any local filesystem restrictions.

All path names in the server (files, directories, folder names, etc.) are Unicode objects. The ubuntuone-syncdaemon should always be able to translate those path names into the local filesystem, supporting any local restrictions, but without altering the name used in the server and other clients (that may run in clients with better filesystems).

At the same time, it should accept any local name and be able to convert it to a valid Unicode object, without altering the real name used in the system.

Example of the former is having in a linux client a filename called "foo: bar", which will be u"foo: bar" in the server, but can not saved as is in a windows client: it should use a different name there, but the server name (and the name used by the linux client) should remain unchanged.

Example of the later is having a path in disk called "foo\xffbar" (in a linux client), that can not be converted to Unicode using UTF-8. So, it must use a different name against the server, but it should remain called like that in the local disk.

To achieve this we will do two changes, mainly:

- start using metadata in the whole client, and translate to a "local name representation" as close as possible to the filesystem calls/events.

- store the "local name representation" as a metadata attribute, if needed; this will not imply a metadata migration: if there, the attribute will be used.

So, the points where we will take care about this is:

- storing partial files while downloading

- saving nodes when downloaded

- finding new nodes in local rescan

- moving files into conflict

- receiveing filesystem notifications

- handling UDFs and shares

Just for reference, we talked a lot about this in bug #368626. What is explained there is a bit different, but it's a good read.

[Facundo Batista (facundo)]

This is deferred to the future.