Tidying up some require and removing overhead caused by sorting

Hi folks,

First of all, please bear in mind that this is my first pull request here. I've read the guidelines but I may have missed something, please point it out.

I know this is a very small change, but I noticed some code in activemodel and activesupport require all files from a specific directory, but they files are sorted before, which does not seem to be useful or needed, and only cause a little overhead when booting rails.
Moreover, the way the files are required is not consistent with the rest of the code.

What do you think ?