Consolidate ProjectIndentifier sorts; drop build support for go1.7

[jmank88]

#672
This change proposes consolidating ProjectIdentifier based sorting code in order to reduce exported API surface, and DRY up internal code.

There were three slightly different methods of ordering ProjectIdentifier:

1. ProjectRoot only
2. ProjectRoot, then Source
3. ProjectRoot, then normalizedSource()

Now the sole Less method behind every sort is the third version.

There is a dependency on sort methods introduced in go 1.8, so CI is expected to partially fail for now.

[ibrasho]

Related: #757

[sdboyer]

we still feel this is relevant, right?

i think, once Go 1.9 is out, i'm fine with abandoning 1.7, so we can actually use sort.Slice().

[jmank88]

I'll have to rebase but it should still be partially relevant

[sdboyer]

we'll hold off on merging this and dropping the 1.7 support until there's a full release of 1.9.

in the meantime, this'll need to drop the 1.7 builder in travis - let's replace that one with 1.9. also, update the README.

[jmank88]

Ok to yank things tagged to build for <=1.7 too?
Edit: I did it.

[sdboyer]

ahh yes, definitely.

…

On 08/18 19:42, Jordan Krage wrote: Ok to yank things tagged to build for <=1.7 too? -- You are receiving this because your review was requested. Reply to this email directly or view it on GitHub: #714 (comment)

[sdboyer]

i think it needs to be just 1.9

[jmank88]

I was holding out for them to update and it looks like they did at some point today. Travis is now recognizing 1.9.x and passing only 1.9 to gimme. Strange that they don't have a general rule for picking up 1.Y.X for any Y though.

[sdboyer]

weee!