Escape regex special characters in tag finder

refs #2149
- Properly highlight tags with special characters ($,[,],^,etc.)
Deduplicate upper-/lowercase tags for posts

server side check for #2478
- added check for duplicate tags in post model
Merge pull request #2496 from halfdan/more-tag-fuddling

Escape regex special characters in tag finder
Ensure generateSlug gets transaction for tags

fixes #2460

- add transacting to tag saving
- add same to users while we're here
Merge pull request #2502 from ErisDS/issue-2460

Ensure generateSlug gets transaction for tags
Merge pull request #2498 from sebgie/duplicate-tags

Deduplicate upper-/lowercase tags for posts
Bump version to 0.4.2-rc2
Merge remote-tracking branch 'upstream/master'