add "junk path" -k option to aapt (DO NOT MERGE)

Adds a "junk path" option to aapt so that you can do:

   aapt add -k archive.zip path/to/some.file

and have the file stored in the zip under the name "some.file"
(without the path).  Needed so that we can use 'aapt add' in place of
'zip -j' when building jar files, which will lead to smaller
incremental OTAs.

(This is a cherry-pick of a change already submitted to eclair-mr2;
the change was approved for mr1.)