Initial 'site.jam' version

[Vladimir Prus]

At this stage site.jam might be very straighforward
- declare a number of features we'd need
- declare somehow rules we need ('make')
- also, there are things like 'MakeLocate' from
Jambase that we definitely need. We must either arrange
for Jambase to make them available even in v2 mode,
or define them outside and either get them in site.jam,
or in initialization code.

[Vladimir Prus]

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We already have enough features/rules for M1, altought they live in 
other places.