Use less offensive language WRT Travise.

Change-Id: I6cfc8a1663940283f047cfb36241ac33433ffbd4
Merge pull request #418 from prometheus/u-c-l/fix-language

Use less offensive language WRT Travis.
Apply a giant code cleanup.

Essentially:

- Remove unused code.

- Make it 'go vet' clean. The only remaining warnings are in generated code.

- Make it 'golint' clean. The only remaining warnings are in gerenated code.

- Smoothed out same minor things.

Change-Id: I3fe5c1fbead27b0e7a9c247fee2f5a45bc2d42c6
Fix typos and import order.

This doesn't make the import order consistend everywhere, just where
it was touched by the previous commit.

Change-Id: I82fc75f8691da9901c7ceb808e6f6fe8e5d62c0e
Merge pull request #421 from prometheus/u-c-l/code-cleanup

Apply a giant code cleanup.
Introduce copy-on-write for metrics in AST.

This depends on changes in:

https://github.com/prometheus/client_golang/tree/cow-metrics.

Change-Id: I80b94833a60ddf954c7cd92fd2cfbebd8dd46142
Add regression tests for metrics mutations in AST.

It turned out in the end, that only drop_common_metrics() produced any
erroneous output in the old system. The second expression in the test
("sum(testmetric) keeping_extra") already worked in the old code, but
why not keep it in...

The way to test ranged evaluations is a bit clumsy so far, so I want to
build a nicer test framework in the end, where all the test cases can be
specified as text files which specify desired inputs, outputs, query
step widths, etc.

Change-Id: I821859789e69b8232bededf670a1b76e9e8c8ca4