I am working on porting geth to [Ubuntu Core](https://developer.ubuntu.com/en/snappy/https://developer.ubuntu.com/en/snappy/). I am testing geth on a Raspberry PI and for Ubuntu Core the $HOME directory is unique for each application. See [here](https://developer.ubuntu.com/en/snappy/guides/filesystem-layout) for more information of their filesystem layout.
For some reason in Go `usr.HomeDir` returns a different value than `$HOME` in Ubuntu Core.
Adding this at the end of `HomeDir()`
```go
fmt.Printf("at HomeDir, user.HomeDir = %s and $HOME is %s\n", usr.HomeDir, os.Getenv("HOME"))
```
gives the following output
```
at HomeDir, user.HomeDir = /home/ubuntu and $HOME is /home/ubuntu/apps/geth.sideload/IJcODREBYbHO
```
With this commit, I propose giving precedence to the `$HOME` environment variable as is also suggested by the [homedir](https://github.com/mitchellh/go-homedir/blob/master/homedir.go) project.
* xeth, rpc: implement eth_getNatSpec for tx confirmations
* rename silly docserver -> httpclient
* eth/backend: httpclient now accessible via eth.Ethereum init-d via config.DocRoot
* cmd: introduce separate CLI flag for DocRoot (defaults to homedir)
* common/path: delete unused assetpath func, separate HomeDir func
