Correct Duplicate Check downloaded TCZs
Correct Duplicate Check downloaded TCZs

If a package folder already exists in tcloop, the tcz file will not be
mounted again. This prevents u-root from over mounting files unnecesarily
when attempting to install a package twice.

u-root/u-root,hugelgupf/u-root,GanShun/u-root,rminnich/u-root,rminnich/u-root,rminnich/u-root,GanShun/u-root,hugelgupf/u-root,u-root/u-root,GanShun/u-root,rminnich/u-root,hugelgupf/u-root,hugelgupf/u-root,u-root/u-root