_emerge: Fix hard-coded emerge-fetch.log locations Bug 520378

Use emergelog._emerge_log_dir instead of the hard-coded paths.
_emerge: Add the missed emerge-fetch.log in previous commit
Wrap fakeroot around MISC_SH_BINARY calls

When feature fakeroot is active all pre/post actions need
to be called with the fakeroot wrapper.

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
dep_zapdeps: fix bug #522652

For cases such as || ( X <A-2 ), where X is unsatisfiable and A-1 is
installed, fix dep_zapdeps to make the correct choice.
Add test for bug #522652 with slot-operator

This test case uses || ( bar foo:= ) syntax that is forbidden by PMS.