l3build: Typeset docs in a dedicated location

I ran into an issue with the latest CTAN release where a file 'here' was
causing issues. By using a dedicated directory, we control what files are
available to the process: in this case, the local files, source file itself
and then system tree if allowed.

At present, the end point here is still to copy PDF files back to the original
location: seems most useful approach but can be altered if required.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5107 de43f980-851b-0410-b2f7-c40aca1f87e0
l3build: Make sure typesetting has exactly the correct files available

Clean out the localdir first so that there is nothing left over, and only
install deps once per module being typeset (most useful for l3kernel).


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5108 de43f980-851b-0410-b2f7-c40aca1f87e0
Revert r5107 and r5108

Life is actually more complicated than the previous commits suggest. There
is a need to worry about multiple source files, and copying them is required
for in e.g. l3kernel to do the job 'properly'. That then makes life more
complex with paths. For the moment, stick with typesetting in place.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@5109 de43f980-851b-0410-b2f7-c40aca1f87e0