after free() unused pages are not exempt

[GoogleCodeExporter]

What steps will reproduce the problem?
1.r13702
2.conf/mods.config
+ include embox.test.mem.heap
3.increase difference beetween ALLOC_FROM and ALLOC_TO, and set ALLOC_COUNT = 1

What is the expected output? What do you see instead?
This test allocates all pages, after that those pages will linked to 
kernel_task, so malloc() in user_task will returns NULL even if size 1.

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Original issue reported on code.google.com by ki.stfu on 8 May 2014 at 1:44