An ebuild for numdiff [1]

This commit provides an ebuild for the numdiff utility, which is yet
another diff-tool for comparic files ignoring small numerical differences

[1] http://www.nongnu.org/numdiff/
Add missing "|| die" and improve mv statements
Merge pull request #109 from tamiko/numdiff

An ebuild for numdiff (http://www.nongnu.org/numdiff/)