Rework diff function

This removes --unified from the default options to make it possible to pass -y
without worrying about conflicting output formats.

diffu has also been added as an alias to make it easier to get output as a
unified diff.

Fixes #1231

modules/utility/functions/diff

@@ -8,14 +8,12 @@
 function diff {
   if zstyle -t ':prezto:module:utility:diff' color; then
     if (( $+commands[colordiff] )); then
-      command colordiff --unified "$@"
-    elif (( $+commands[git] )); then
-      git --no-pager diff --color=auto --no-ext-diff --no-index "$@"
+      command colordiff "$@"
     else
-      command diff --unified "$@"
+      command diff "$@"
     fi
   else
-    command diff --unified "$@"
+    command diff "$@"
   fi
 }
 

modules/utility/init.zsh

@@ -49,6 +49,7 @@ alias sftp='noglob sftp'
 alias _='sudo'
 alias b='${(z)BROWSER}'
 alias cp="${aliases[cp]:-cp} -i"
+alias diffu="diff --unified"
 alias e='${(z)VISUAL:-${(z)EDITOR}}'
 alias ln="${aliases[ln]:-ln} -i"
 alias mkdir="${aliases[mkdir]:-mkdir} -p"