got bash completion working for "git annex" not just "git-annex"

This needs a patch to git to cause the git-annex completion to be
auto-loaded when completing "git annex <tab>". Otherwise, it will only
load when "git-annex" is tab completed. Once loaded, it works for both
uses. I've submitted the git patch to the git mailing list.

bash-completion.bash

@@ -0,0 +1,25 @@
+# Use git-annex's built-in bash completion
+# This bash completion is generated by the option parser, so it covers all
+# commands, all options, and will never go out of date!
+source <(git-annex --bash-completion-script git-annex)
+
+# Called by git's bash completion script when completing "git annex"
+_git_annex() {
+    local cmdline
+    CMDLINE=(--bash-completion-index $(($COMP_CWORD - 1)))
+
+    local seen_git
+    local seen_annex
+    for arg in ${COMP_WORDS[@]}; do
+        if [ "$arg" = git ] && [ -z "$seen_git" ]; then
+		seen_git=1
+		CMDLINE=(${CMDLINE[@]} --bash-completion-word git-annex)
+	elif [ "$arg" = annex ] && [ -z "$seen_annex" ]; then
+		seen_annex=1
+	else
+		CMDLINE=(${CMDLINE[@]} --bash-completion-word $arg)
+	fi
+    done
+
+    COMPREPLY=( $(git-annex "${CMDLINE[@]}") )
+}