Merged from trunk 4816:4828

Merged from trunk 4816:4828

For bug #152726, ignore hidden files in vardbapi.cp_list().

For full compatibility with older versions of portage, write the path in
the serialized _eclasses_ when possible.

Fix broken is_eclass_data_valid comparison logic.

Test for basestring instead of types.DictType so that the test more
generic.

Reverse the relationship between __contains__ and has_key in all cache
classes since python handles the "in" operator more efficiently than a
has_key method call.

Streamline portage pythonpath handling and add an override analog to how
the bash side does it.

rename getmaskingreason() to getpmaskcomment() to clarify its function,
report each license as a separate mask instead of combining them all
together into a single value for getmaskingstatus()

need a mutable config instance to use setcpv

add function getlicensetexts() to extract license texts relevant to a
given cpv (to be used by emerge masked by display)

show licenses or pointer to license files on 'masked by' message

svn path=/main/branches/prefix/; revision=4831