Please bump monotone. 0.47 was released Sun Mar 14 21:15:06 UTC 2010. 0.46 was released Sun Jan 17 21:40:35 UTC 2010. The latter added several new commands, "bisect" among them. See http://www.monotone.ca/NEWS for more details.
After renaming the ebuild from 0.45 to 0.47 and dropping the src_prepare function as the patch mentioned therein is included in the new release, monotone emerged on my system.
17 May 2010; Peter Volkov <pva@gentoo.org> +monotone-0.47.ebuild, metadata.xml: Version bump, bug #309577, thank Jack Lloyd for report.