tmux stays in current working directory on split

Most versions of tmux will keep you in the same working directory when splitting
the screen or creating a new window; this makes it explicit. This now works on
any modern tmux on all platforms.
Rehauled vimrc for editing TeX files

No longer using vim-latexsuite. Instead I've tried to recreate the few nifty
completions it provided by using some extra autocommands and substitutions. I
also removed a minor redundant line of code in the installation Makefile.
Fancy new bash programmable completions

I now have a special file for custom bash completions, which for some reason
does not work with my bash in Arch. It gets sourced in the bashrc, but before
the default bash completion script to let the defaults override them if they
already exist. The completions for evince and pdflatex should make writing LaTeX
much less irritating.

The 'open' alias in bash_aliases is now a function. This allows us to
automatically redirect output to /dev/null, since most of the time we're opening
some sort of media.