Fix debian bug#762436: :default-registry was broken in ASDF 3.1.
Test case: at the make load REPL, evaluate
(initialize-source-registry '(:source-registry :default-registry :ignore-inherited-configuration))
Bump version to 3.1.3.9
Fixed broken gitweb links.
Improve docstrings for directory functions.
Bump version to 3.1.3.10