Fixing "save_info" behavior on themes

When using save_info it actually writes the file into fuel/app/config/{theme info filename} instead the respected theme's directory, if you look at line 619 (load_info function) you'll notice it passes array($theme) instead of array($theme['name']) this causes an inconsistent behavior between reads and writes.

This is applicable to 1.7.X as well.
Merge pull request #1685 from Destreyf/patch-2

Fixing "save_info" behavior on themes