Follow gopkg.in URL churn
.gitignore: Ignore cram error files and any "go build" output
cram: Explicitly set umask where it matters
cram: Avoid globally configured git filters tripping up tests

build.t makes sure no extra files are created in the cache directory.
If global git config sets a filter, said filter is triggered by the
code fetched by "go get", and the filter is implemented by a demand
script, the resulting executable will end up there, too.

Overriding XDG_CONFIG_HOME makes git not use the global configuration,
and avoids this issue. Hopefully the "go get" completes without git
configuration.
cram, testutil: Make sure argv[0] is what we expect

Use `demand -gopath` so the tests work even before a push, for easier
development.
cram, testutil: Use bundled test utility and -gopath to speed up tests
Make argv[0] point to executable, not specfile
cram: Make tests know less about cache implementation
Reorder open and readlink, so maybeReadlink doesn't need to handle ENOENT
cram: Avoid globally configured git filters tripping up tests, part 2

If global git config sets a filter, said filter is triggered by the
code fetched by "go get", and the filter is implemented by a demand
script, the filter ends up being rebuilt from scratch for no good
reason.

Overriding XDG_CONFIG_HOME makes git not use the global configuration,
and avoids this issue. Hopefully the "go get" completes without git
configuration.

This is similar to abdd4def731ae4749fa44424aa2d15e5bc0522a9 but about
test speed, not correctness.
Typo in error message