[m2e-dev] Support for maven-tiles (and lifecycle participants)

[carsten.pfeiffer@xxxxxxxx]

Hi,

we'd like to get m2e to support the
maven-tiles plugin, as requested in 
https://github.com/repaint-io/maven-tiles/issues/9

As lifecycle participants are generally
not supported by m2e, we came up
with the idea to add an explicit extension
point for lifecycle participants, to
explicitly enable certain plugins. So
far, we call afterProjectsRead() on them. 

That way, we could implement an m2e-extension
that allows the maven-tiles plugin
to successfully participate in the (m2e-)
build.

For reference, there have been other
requests about lifecycle participants, which
might benefit from this:
- https://dev.eclipse.org/mhonarc/lists/m2e-dev/msg01754.html
- http://dev.eclipse.org/mhonarc/lists/m2e-users/msg05090.html
- http://dev.eclipse.org/mhonarc/lists/m2e-dev/msg00822.html

Only one other fix was necessary to
make it work: when an error occurs, the
current version of the maven-tiles plugin
does not provide location information
for the error and m2e then fails with
an NPE.

We have the code at https://github.com/GEBIT/m2e-core/commits/lifecycle-participant
for the time being, but if you think
this is a good idea and worthy to be added to m2e,
we can push the changes to gerrit.

Thanks
Carsten