Quickbook: Rough stab at outputting dependencies. Refs #6691
Adds --output-deps flag. To write out dependencies to deps.txt:
quickbook --output-deps deps.txt source.qbk
If --output-deps is specified, quickbook won't generate an output file
unless one is specified with --output-file. If there is an error it
will return an error code, but it will still write out all the opened
files.
Known issues:
- If the same file is included/imported twice it may or may not list it
twice. Should be consistent.
- Doesn't include SVG files. It probably should as they can affect the
output.
- Need to check some of the path issues for things such as xinclude
paths which depend on the output file path.
- Needs tests and documentation.
