Cleanup parsing of packages.

This diff is loosely based on a patch by Jo-Philipp Wich <google@wwsnet.net>
posted in the bugtracker (Issue #24). Peak memory consumption while parsing
package lists is dramatically reduced.

Thanks to Camille Moncelier for fixing problems after reallocing for long lines.

git-svn-id: http://opkg.googlecode.com/svn/trunk@283 e8e0d7a0-c8d9-11dd-a880-a1081c7ac358