Restrict name matching to first 8 characters

[Gaerzi]

Example: textcolors.txt in zdoom.pk3 should match file name textcolo. (Without the current cheat of having match_name = "textcolo", "textcolors";.)

[sirjuddington]

It might be a better idea to allow wildcards in the match_name property (eg. "textcolo*"). Only issue here would be speed concerns.

[Gaerzi]

Problem came from people who had lumps with names like textures_sprites.txt and so on. It works in ZDoom because it only looks at the first eight characters of the name.