fix(helm): avoid a panic for sign

Before this fix:

```
 /Users/philips/src/k8s.io/helm/bin/helm package --sign mychart --key FC8A365E
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0x13120a]

goroutine 1 [running]:
panic(0x10fed00, 0xc4200120d0)
       	/usr/local/Cellar/go/1.7.1/libexec/src/runtime/panic.go:500 +0x1a1
k8s.io/helm/pkg/provenance.(*Signatory).ClearSign(0xc4205db100, 0xc42011ec20, 0x20, 0x8, 0xc4205db100, 0x0, 0x0)
       	/Users/philips/src/k8s.io/helm/pkg/provenance/sign.go:156 +0x3a
main.(*packageCmd).clearsign(0xc420017720, 0xc42011ec20, 0x20, 0x0, 0x0)
       	/Users/philips/src/k8s.io/helm/cmd/helm/package.go:143 +0xa5
main.(*packageCmd).run(0xc420017720, 0xc420390240, 0xc420120d00, 0x1, 0x4, 0x13639b0, 0x104dfe0)
       	/Users/philips/src/k8s.io/helm/cmd/helm/package.go:130 +0x31b
main.newPackageCmd.func1(0xc420390240, 0xc420120d00, 0x1, 0x4, 0x0, 0x0)
       	/Users/philips/src/k8s.io/helm/cmd/helm/package.go:77 +0xc4
k8s.io/helm/vendor/github.com/spf13/cobra.(*Command).execute(0xc420390240, 0xc420120c40, 0x4, 0x4, 0xc420390240, 0xc420120c40)
       	/Users/philips/src/k8s.io/helm/vendor/github.com/spf13/cobra/command.go:571 +0x234
k8s.io/helm/vendor/github.com/spf13/cobra.(*Command).ExecuteC(0xc420405200, 0x0, 0x0, 0x0)
       	/Users/philips/src/k8s.io/helm/vendor/github.com/spf13/cobra/command.go:661 +0x367
k8s.io/helm/vendor/github.com/spf13/cobra.(*Command).Execute(0xc420405200, 0x1b52720, 0xc4200001a0)
       	/Users/philips/src/k8s.io/helm/vendor/github.com/spf13/cobra/command.go:620 +0x2b
main.main()
       	/Users/philips/src/k8s.io/helm/cmd/helm/helm.go:110 +0x2d
```

fix(Makefile): cleanup _dist files

fix(lint): allow .txt files

closes #1161

feat(charts): add 'dependencies:' to Chart.yaml

fix(tiller): store failed release on post-inst failure

feat(release): remove tiller from cross compile

fix(kube): delete should skip resources not found

This feature adds a dependencies section to a chart file. It is a
prerequisite for adding automated chart management tooling as described
in #874.

fix(helm): removed debug output

This fixes a bug where post-install hooks did not result in recording a
failure.

Also fixed a bug where a `--dry-run` will result in an error because
of the recently added status support.

There are several other output inconsistencies that I noticed and filed
as issue #1135.

Closes #1130

fix(tiller): Install --replace will result in an upgrade

If a release has been deleted, `install --replace` will work but the release
status will still be "deleted". This means that subsequest attempts to
change the release will fail. Upgrading the release instead will prevent
such zombie releases.

Closes #1131

feat(rollback-support): add version field to protos

chore(tiller): delete redundant testing of storage in pkg/environment

fix(tiller): return status for deleted release

This modifies `helm status` to return info about deleted and failed
releases. We do our best to retrieve info for releases that were
partially deployed.

print the status after install/upgrade

fix(helm): make repo index not require repo_url

fix(helm): make repo remove, clear cache

minor engine unit test fix

Signed-off-by: vaikas-google <vaikas@google.com>

First cut of handling NOTES.txt file

feat(cmd): install latest tagged image on `helm init`

closes: #1117