Start to generalize trivial-validate.py input

Previously. trivial-validate.py took either a single specified
file or all the files in a specified directory. Seth pointed out
that we can generalize it to take a list of files / directories.
Merge single and multi file trivial validation

1. Add option --dupdir to specify where to check for duplicate rulesets
if this is not among the rulesets being validated.

2. Remove distinction between single and multi file validation.

3. Error handling for non-ruleset xml files and rulesets that are not
named.
Enable validation by specifying filenames
Removing unused filetree traversal function
Fix bug in duplicate ruleset checking
Remove extra output for debugging
Replace '/'.join with os.path.join