Allow inheritance for directory permissions

[blee]

Currently, directory permissions get copied into every single module that contains files in those directories.

This is limiting for modules whose only meaningful purpose is to install files.

Consider the following:

• module base1, which installs directory /dir with mode 0755
• module base2, which installs directory /dir with mode 0700
• module sampleconf, which installs file /dir/sample.conf but does not care about the permissions on /dir
• recipe r1, with contents base1 sampleconf
• recipe r2, with contents base2 sampleconf

There should be a way for the permissions on /dir to be "inherited" from modules base1 and base2, i.e. machines using recipes r1 and r2 would have different permissions on /dir.