If the starting index is beyond the end of the list, it's a programming
error. Previously, the code was trying to raise a runtime error, but
actually causing a segfault.
This was detected by test code in test-mutable-tree.c, which is removed
in this commit because it should now not be possible to crash here.
https://bugzilla.gnome.org/747032
The tar files we're making of artifacts don't include parent
directories. Now we could change the builder to make them, but we can
also just autocreate them on import. Mode 0755 with no xattrs seems
OK here.
It's pretty trivial to map a previously existing commit tree into a
mutable tree too. While we're here change the command line arguments
for commit so that we can now properly overlay any combination of
directory, commit, or tarfile.
Matthew Barnes
Sam Thursfield
Colin Walters