util: show all dirty status indicators

Summary: Instead of just showing `?` or `*`, show one of each symbol in the
dirty status.  This means there will be a maximum of 5 characters at the end of
the prompt, which is fine.

Test Plan: N/A

Question for reviewer: I am having trouble running the test suite for Sapling.
I'd appreciate some help getting this working.  I can provide more details if
you wouldn't mind helping

eden/scm/contrib/scm-prompt.sh

@@ -162,10 +162,9 @@ _hg_prompt() {
 # cf. https://www.internalfb.com/intern/qa/4964/how-do-i-show-the-mercurial-bookmarkgit-branch-in?answerID=540621130023036
 _hg_dirty() {
   if [ -n "${SHOW_DIRTY_STATE}" ] &&
-     [ "$(hg config shell.showDirtyState)" != "false" ]; then
-    command hg status 2> /dev/null \
-    | command awk '$1 == "?" { print "?" } $1 != "?" { print "*" }' \
-    | command sort | command uniq | command head -c1
+     [ "$(sl config shell.showDirtyState)" != "false" ]; then
+       sl status 2> /dev/null \
+         | awk '{printf " "} {print $1}' | sort | uniq | paste -sd ' ' -
   fi
 }