added support for bazaar in agnoster theme (#5016)

the agnoster theme is now able to render basic information
if the user is currently residing inside a bazaar folder.
if so, it will render a green promt segment with "bzr" and
the current revision number in it. if there are untracked
files, the bar will be rendered in yellow. if there are
changes to already tracked files, a + character will be
printed.

themes/agnoster.zsh-theme

@@ -127,6 +127,27 @@ prompt_git() {
   fi
 }
 
+prompt_bzr() {
+    if (bzr status >/dev/null 2>&1); then
+        status_mod=`bzr status | head -n1 | grep "modified" | wc -m`
+        status_all=`bzr status | head -n1 | wc -m`
+        revision=`bzr log | head -n2 | tail -n1 | sed 's/^revno: //'`
+        if [[ $status_mod -gt 0 ]] ; then
+            prompt_segment yellow black
+            echo -n "bzr@"$revision "✚ "
+        else
+            if [[ $status_all -gt 0 ]] ; then
+                prompt_segment yellow black
+                echo -n "bzr@"$revision
+
+            else
+                prompt_segment green black
+                echo -n "bzr@"$revision
+            fi
+        fi
+    fi
+}
+
 prompt_hg() {
   (( $+commands[hg] )) || return
   local rev status
@@ -198,6 +219,7 @@ build_prompt() {
   prompt_context
   prompt_dir
   prompt_git
+  prompt_bzr
   prompt_hg
   prompt_end
 }