#17 prefix string to new entries in archive

[LynX]

Hello,

This patch provides support of adding new files to archive under specific entry.
The purpose of such support can be found in http://www.info-zip.org/phpBB3/viewtopic.php?f=3&t=368.
The patch was done against latest available sources zip31c.
I would be grateful for any review/comments.

Thank you,
LX

[LynX]

add new file under specific entry