Complete initialization behaviour

[Vladimir Prus]

We'd need to
- import site.jam/user.jam
- get build request from command line and exand it
- get project target for the project in "." and 
pass each element of the exanded build request to it.

The part that needs some thought is getting build
request from the commnand line. Can we use only
"--build", or is "--toolset" required also? How
default set of toolsets will be specified?