l3build: Allow extensions to include "-"


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5268 de43f980-851b-0410-b2f7-c40aca1f87e0
l3build: Run all tests fro "check <name>" as standard

This brings the check function into line whether a file name is given or
not, in the sence that without an engine all tests are now run in all
cases. The question of "build check pdftex" is still to consider: it's arguable
that this should be left alone.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5269 de43f980-851b-0410-b2f7-c40aca1f87e0
Add comment to code for previous commit


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5270 de43f980-851b-0410-b2f7-c40aca1f87e0