Add function gitflow_has_prefixes_configured(), to check whether a repo is
fully initialized for use with gitflow.

Add a means of only asking for the missing gitflow definitions, not all.
(Of course, redefining all is always possible using the -f (--force) flag
of init.)
diff --git a/gitflow-common b/gitflow-common
index 8aaa357..6e5056e 100644
--- a/gitflow-common
+++ b/gitflow-common
@@ -49,12 +49,20 @@
 	[ "$develop" != "" ] && gitflow_local_branch_exists "$develop"
 }
 
+gitflow_has_prefixes_configured() {
+	git config --get gitflow.prefix.feature >/dev/null 2>&1     && \
+	git config --get gitflow.prefix.release >/dev/null 2>&1     && \
+	git config --get gitflow.prefix.hotfix >/dev/null 2>&1      && \
+	git config --get gitflow.prefix.support >/dev/null 2>&1     && \
+	git config --get gitflow.prefix.versiontag >/dev/null 2>&1
+}
+
 gitflow_is_initialized() {
-	gitflow_has_master_configured && \
-	gitflow_has_develop_configured && \
-	# they should be different
-	[ "$(git config --get gitflow.branch.master)" != \
-	  "$(git config --get gitflow.branch.develop)" ]
+	gitflow_has_master_configured                    && \
+	gitflow_has_develop_configured                   && \
+	[ "$(git config --get gitflow.branch.master)" !=    \
+	  "$(git config --get gitflow.branch.develop)" ] && \
+	gitflow_has_prefixes_configured
 }
 
 # get all available branches