Don't just take the last argument, take the first.

This patch was originally contributed as a workaround for the cases
where there were flags that took the first argument position.  This fix
was just plain wrong and this commit reverts it.
diff --git a/git-flow-feature b/git-flow-feature
index 8893598..b69cc73 100644
--- a/git-flow-feature
+++ b/git-flow-feature
@@ -180,7 +180,7 @@
 	parse_cmdline "$@"
 
 	# read arguments into global variables
-	NAME=$(last_arg "$@")
+	NAME=$1
 	BRANCH=$PREFIX$NAME
 }