Proposed fix for issue #1145

[aikebah]

Fixes Issue #1145

Description of Change

• Implemented single-pass multi-xml-schema-validating parser similar to existing code for hints parsing
• Added new suppression xmlschema version with the 'until' for a suppression rule implemented as attribute of suppress (which seems more logical to me than a child element)
• updated code to support this temporary suppression of issues
• Added testcases for the proper parsing of the version 1.1 (existing) and 1.2 (new) suppressionfile xmlschema

Have test cases been added to cover the new functionality?

yes (validating that suppressions with until 'in-the-past' do not appear in the suppression-rules and suppressions without until and with until 'in-the-future' do appear in the suppression-rules after parsing)

[aikebah]

@jeremylong Let me know if you'd rather have a PR from a rebased version to pass the travis-ci build (with a proper NVD datafeed configuration)

[jeremylong]

@aikebah if you wouldn't mind rebasing this - I would appreciate it.

Thanks!

[aikebah]

branch rebased to current master