unit blacklist was apparently added back in r13176 for 1.8.3. unfortunately, this did not get in the whatsnew pages. that makes it complicated to mention to users that this feature is available for some period of time.
even though it's all old, let's add a quick note in https://www.zabbix.com/documentation/1.8/manual/about/what_s_new_1.8.3 about unit blacklist being added with units '%', 'ms' and 'rpm'
uppercase RPM was added in r19289 as part of
ZBX-3677 - that's at least mentioned in the changelog