POM editor does not ask Team Provider to make pom.xml writable

When having Perforce as Team provider, files are normally read-only.

When starting editing a file, the Perforce plugin (P4WSAD) will transparently open it for edit.

This does not happen with the POM editor in m2eclipse however (except when you edit in the pom.xml tab).

The POM editor must check if pom.xml is read-only, and if so ask the team provider (if any) to make it writable.

It must not silently ignore that the file is read-only.