bash completion for brew list --multiple

As per 9ab605c7f1883 removal of `brew dirty`. `--multiple` *implies*
`--versions`, thus IMO it shouldn't be necessary to also explicitly
include the `--versions` option, but that's a separate matter. For now
this offers the small added convenience of:

    $ brew list --m<TAB><TAB>

to quickly expand the `brew dirty` equivalent.

Closes Homebrew/homebrew#29571.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Library/Contributions/brew_bash_completion.sh

@@ -282,25 +282,38 @@ _brew_linkapps ()
 
 _brew_list ()
 {
+    local allopts="--unbrewed --verbose --pinned --versions --multiple"
     local cur="${COMP_WORDS[COMP_CWORD]}"
+
     case "$cur" in
     --*)
-        # options to brew-list are mutually exclusive
+        # most options to brew-list are mutually exclusive
         if __brewcomp_words_include "--unbrewed"; then
             return
         elif __brewcomp_words_include "--verbose"; then
             return
         elif __brewcomp_words_include "--pinned"; then
             return
+        # --multiple only applies with --versions
+        elif __brewcomp_words_include "--multiple"; then
+            __brewcomp "--versions"
+            return
         elif __brewcomp_words_include "--versions"; then
+            __brewcomp "--multiple"
             return
         else
-            __brewcomp "--unbrewed --verbose --pinned --versions"
+            __brewcomp "$allopts"
             return
         fi
         ;;
     esac
-    __brew_complete_installed
+
+    # --multiple excludes formulae and *implies* --versions...
+    if __brewcomp_words_include "--multiple"; then
+        __brewcomp "--versions"
+    else
+        __brew_complete_installed
+    fi
 }
 
 _brew_log ()