Bugzilla bug 301249: a better way to determine if NSS_CO_TAG can be pulled

by date.  a=benjamin.smedberg.

client.mk

@@ -540,11 +540,11 @@ ifdef MOZ_CO_FLAGS
 endif
 NSS_CO_FLAGS := $(NSS_CO_FLAGS) $(if $(NSS_CO_TAG),-r $(NSS_CO_TAG),-A)
 
-# Cannot pull static tags by date
-ifneq (,$(findstring _RTM,$(NSS_CO_TAG))$(findstring _TAG,$(NSS_CO_TAG)))
-CVSCO_NSS = $(CVS) $(CVS_FLAGS) co $(NSS_CO_FLAGS) $(NSS_CO_MODULE)
-else
+# Can only pull the tip or branch tags by date
+ifeq (,$(filter-out HEAD %BRANCH,$(NSS_CO_TAG)))
 CVSCO_NSS = $(CVS) $(CVS_FLAGS) co $(NSS_CO_FLAGS) $(CVS_CO_DATE_FLAGS) $(NSS_CO_MODULE)
+else
+CVSCO_NSS = $(CVS) $(CVS_FLAGS) co $(NSS_CO_FLAGS) $(NSS_CO_MODULE)
 endif
 
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