oh-my-fish.fish: ensure duplicates aren't prepended to fish_function_path
oh-my-fish.fish: remove debug code thanks @GlitchMr
oh-my-fish.fish: add helper function to test directory

- existence of dir
- and also if it is already in the path list
oh-my-fish.fish: remove unneeded code
using 2 spaces instead of 4 spaces
Merge pull request #82 from theonewolf/fix-duplicating-function-path