I tried to re-install m2eclipse, but it tells me that the install failed because m2eclipse is already installed.
I went so far as to un-install Eclipse and start over from scratch, but with the same results.
In the Atlassian SDK instructions, it says that if you have Eclipse without the m2eclipse plugin, then:
If you are using Eclipse without the M2Eclipse plugin:
* Run the following command: atlas-mvn eclipse:eclipse
* Then configure your workspace with the Maven repository location: