Dep: Consolidate fs.go, internal/fs.go, and gps/internal/fs/fs.go

[sdboyer]

fs.go and gps/internal/fs/fs.go contain a lot of duplicate code, back from when they were completely separate projects. They should be consolidated into a single internal/fs subpackage.

While we're at it, let's also rearrange internal/fs.go into the same internal/fs subpackage.

[sdboyer]

Note - this will break gps' encapsulation, as it'll be reaching up into github.com/golang/dep/internal/fs for these functions. In general, I want to keep that encapsulation intact, but it's OK to make an exception here for these functions, which are likely to always remain internal, and that we really _don't_ want to duplicate.

[vedhavyas]

I can take this up @sdboyer

[sdboyer]

@vedhavyas woohoo, awesome! though looks like @ibrasho may have beat you to it - but we've got issues popping out left and right currently, i'm sure there'll be another one coming up soon 😄

[curtisallen]

now that #547 is closed should this ticket be closed?

[sdboyer]

ah yes, thanks!