improve command-line options output

- 3 new categories
 - Connection options
 - Testing options
 - RPC server options
- rename "SSL options" to "RPC SSL options"
- append "on startup" to
 - checklevel
 - loadblock
 - reindex
 - rescan
 - salvagewallet
 - upgradewallet
- Fix rpcuser and rpcpassword appeared twice for bitcoind in rpcclient.cpp


![usage](https://f.cloud.github.com/assets/2814559/2062802/ac807722-8c9f-11e3-9525-f4c10287905a.png)