Failed to validate extension that depends on com.atlassian.sal:sal-api

I have a fix which cover the described problem by forcing to use the dependency type in all cases.

I was hoping to have time to implement something a bit more complete, especially by actually getting the atlassian-plugin extension handler to check the default file extension and notice it was the same as the one requested by the dependency, but this will have to be done later as part of XCOMMONS-3027.