[PATCH] Fix VFS to write mod data correctly

[historic_bruno]

The VFS can associate many real paths with a single virtual path, which is how e.g. mods work. This is correct for reading, it makes sense that the VFS can read files from one of the several real paths in some defined order. However, for writing files, this is incorrect behavior, there should be a single well-defined real path for writing a file to a given virtual path.

This results in problems like #895, where the mod data may be in a read-only directory or in an archive, the write fails and causes the game to crash.

The desired behavior is as follows:

• For SVN/Git users, mod data is saved directly within the game's data directory (e.g. binaries/data/mods/public) - always a writable location. This is a convenience for devs, so they can modify the game's data and commit back to the repo.
• For everyone else, mod data is saved in the user mod directory (see GameDataPaths) - also a guaranteed writable location.

[leper]

The attached patch writes to the user mod directory if a config/dev.cfg file is not present. Otherwise it writes to the game data directory of the last mod that has a directory in there. This is not really optimal if a dev wants to keep one of his mods in the user mod directory.

Something missing from the patch is the exclusion of the dev.cfg file from the archive builder for releases.

(testing this should be done with -noUserMod) (maybe that should be implied by the presence of the dev.cfg file)

Any input on how to handle the dev case would be appreciated.

[leper]

Thinking about mods present in both directories (user mod and binaries/) it'd be better to mount them with different priorities to make this more explicit, instead of relying on the date of the file or the file loader precedence. I'll attach a new patch.

[leper]

Dev implies -noUserMod. Exclude dev.cfg from release packaging. Updated to work properly with mods present in both mod folders

[historic_bruno]

Looks good, here's a few comments:

• We can add a comment to dev.cfg explaining its purpose
• dev.cfg should be excluded from the OS X bundle in build-osx-bundle.sh
• The mods variable on line 465 of GameSetup.cpp could be a const?

I don't really like the inconsistency in the dev and non-dev cases, in terms of mounting the read-only and user-writable mods, but I can't think of a better way of doing it yet. It's already a big improvement over what we have, so I say commit it :)

[leper]

In 13472:

Write mod data correctly. Fixes #1940.