Also, improve reporting of version resolution. e.g.:
```
$ ./emsdk install sdk-latest
Resolving SDK alias 'latest' to '2.0.23'
Resolving SDK version '2.0.23' to 'sdk-releases-upstream-77b065ace39e6ab21446e13f92897f956c80476a-64bit'
Installing SDK 'sdk-releases-upstream-77b065ace39e6ab21446e13f92897f956c80476a-64bit'..
...
```