Hide the notes about readline-devel

Since readline is the last package go-gotten, it appears to users that
the install has failed, and sends them looking for how to install
readline and why the install isn't working, when in fact the go module
has installed just fine.

This uses a little make trickery to not give any indication that
anything's wrong unless the install fails.

Makefile

@@ -136,14 +136,20 @@ go_get_client_deps: go_get_common_deps
 	$(GOGETTER) camlistore.org/pkg/misc/gpgagent
 	$(GOGETTER) camlistore.org/pkg/misc/pinentry
 ifeq ($(OS),darwin)
-	$(GOGETTER) github.com/bobappleyard/readline
-	echo 'make sure that you have readline installed via {port,brew} install readline'
+	@echo $(GOGETTER) github.com/bobappleyard/readline
+	@if ! $(GOGETTER) github.com/bobappleyard/readline; then \
+		echo 'make sure that you have readline installed via {port,brew} install readline'; \
+		exit 1; \
+	fi
 endif
 ifeq ($(OS),linux)
-	$(GOGETTER) github.com/bobappleyard/readline
-	echo 'make sure that you have readline installed via:'
-	echo '* yum install readline-devel'
-	echo '* apt-get install libreadline-dev'
+	@echo $(GOGETTER) github.com/bobappleyard/readline
+	@if ! $(GOGETTER) github.com/bobappleyard/readline; then \
+		echo 'make sure that you have readline installed via:'; \
+		echo '* yum install readline-devel'; \
+		echo '* apt-get install libreadline-dev'; \
+		exit 1; \
+	fi
 endif
 
 go_get_deps: go_get_common_deps go_get_agent_deps go_get_platform_deps go_get_client_deps