Update tag check in release-hook to prevent false positives

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Makefile.am

@@ -37,7 +37,7 @@ endif
 # Check if tagged in git
 #
 release-hook:
-	@if [ ! `git tag | grep $(PACKAGE_VERSION)` ]; then				\
+	@if [ ! `git tag -l v$(PACKAGE_VERSION) | grep $(PACKAGE_VERSION)` ]; then	\
 		echo;									\
 		printf "\e[1m\e[41mCannot find release tag $(PACKAGE_VERSION)\e[0m\n";	\
 		printf "\e[1m\e[5mDo release anyway?\e[0m "; read yorn;			\