New functionscan_deps() to auto-detect package dependencies from
R code.deps::. automatically uses detected dependencies now if no
DESCRIPTION file is found.

pkgdepends now does not restore ownership when uncompressing.tar.gz
files. This works better on sshfs and other file systems that do not
have proper Unix permissions.

The dependency solver now uses better heuristics, that works better
(=faster) with multiple repositories with large overlaps (#392).