Mark directories as order-only prerequisites.
Refactoring.

Return lists instead of strings from lower-level routines, and remove some
unnecessary local variable declarations and assignments.
Refactoring.

Name helper functions more clearly and give them a purpose rather than being
simply helpers for the main code.
Introduce 'deps' subcommand.

This subcommand prints out the dependencies of a group in topologically sorted
order.  Additionally, all include directives are topologically sorted.
Wrap 'LICENSE'.
Reformat README.
Merge remote-tracking branch 'frutiger/master'

Conflicts:
	bde-meta.py
Add sorted linkline to 'cflags'