Use .vfsforgit instead of .gvfs directories for GVFS provider

[chrisd8088]

In order to avoid conflicts with GNOME VFS (GVfs) and pre-existing .gvfs directories on Linux systems -- not to mention user confusion -- we need the GVFS provider to create and use .vfsforgit* hidden directories instead of its current .gvfs* ones. This could be exclusive to the Linux client, though.

See microsoft#987.

[kivikakk]

microsoft#1084 will pave the way for this.

[kivikakk]

Assigning myself -- I'll take care of the rebase to use the new functionality once microsoft#1084 is merged!

[kivikakk]

microsoft#1125 now uses the functionality to use ".vfsforgit" as the folder name on Linux.

[kivikakk]

Closing per other tickets merged into microsoft#1125.