Property and path utilities

[Vladimir Prus]

1. Complete property.as-path rule, which is used to 
generate path representation of properties.

2. Write a rule which will compute a path where
a target should be stored. At this stage, I suggest
to make it simple -- just use 
"bin/main-target/<properties>, where <properties>
are what "as-path" returns. This logic should be
plugged to virtual-target.actualize rule (now around
line 334). I also suggest that we don't bother about
intermidiate target paths, as I have some thoughts
about them which will post after holidays.

[Vladimir Prus]

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I've suddenly realized that this issue is already fixed.