File attributes are not being correctly applied on Linux

[fireflycons]

It has been found that although the zip appears to contain rwxrwxrwx on each file, when unzipped the files end up with rw-rw-rw- which is not good if some of the content is ELF binaries or shebanged script files.

[fireflycons]

Further investigation yields that SharpZipLib was not setting the Host OS field of each zip file entry, leaving it as a DOS/Windows type, and that Unix/Linux unzippers ignore file attributes if the Host OS field isn't Unix.

Release 1.2.0 of SharpZipLib addresses this, allowing the caller to set this.

icsharpcode/SharpZipLib#325