refactor(pebuild): use iterators where lists aren't required
docs(ebuild/processor): minor spelling and grammar fixes
fix(pmaint): drop repeated 'in' from regen message
refactor(portage_conf): use cache root dir perms to determine writability

If the cache directory has permissions set allowing for writes to occur
they are allowed. Previously this was set via the readonly parameter to
the related mk_simple_cache function.
refactor(ebuild/portage_conf): set full md5-dict cache dir in config

Previously the full path was constructed in the initialization method
related to the md5_cache class, but this simplifies things and allows
the readonly check from the previous commit to work properly starting
from the root cache dir.