Try to extend goimports

[kamilsk]

I propose to make goimports little bit more strict.

For example, an input is

import (
	"context"
	"github.com/pkg/b"
	"github.com/pkg/a"

	"github.com/pkg/y"
	"github.com/pkg/x"
	"github.com/pkg/z"
)

After goimports it looks like

import (
	"context"

	"github.com/pkg/a"
	"github.com/pkg/b"

	"github.com/pkg/x"
	"github.com/pkg/y"
	"github.com/pkg/z"
)

I don't have a possibility to transform it into something like this

import (
	"context"

	"github.com/pkg/a"
	"github.com/pkg/b"
	"github.com/pkg/x"
	"github.com/pkg/y"
	"github.com/pkg/z"
)

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[kamilsk]

I signed it!

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This PR (HEAD: fcc3616) has been imported to Gerrit for code review.

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[gopherbot]

Message from Brad Fitzpatrick:

Patch Set 1: Code-Review-2

Sorry, I don't want to add more options.

The existing configurability is a bit regrettable.

If you want this ungrouping functionality, it could live in a separate tool.

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[gopherbot]

This PR is being closed because golang.org/cl/156057 has been abandoned.