Remove hard tab characters wherever possible

For historical reasons, many parts of the RT code intermix hard tabs and
siace-based indentation.  This commit does not attempt to standardize
indentation, merely the horrid intermixing of hard tabs and spaces.

A few hard tabs remain in t/mail/mime_encoding.t and t/mail/outlook.t,
as the tabs are within strings representing test data; they also remain
in third-party source.

Best viewed with the -w option to `git diff`.
Replace hard tabs with \t in test strings
Add a policy test to enforce lack of tabs for BPS files
Fix copyright check to run against content, not $_
Factor out other copyright check to only apply to css and js files

This removes false-positives, such as on t/99-policy.t itself, which
contains the word "copyright".
Only skip tab detection if there was a different copyright, regardless of if we require our own
Switch to using done_testing
Merge branch '4.2/untabify'

Conflicts:
	lib/RT/Record.pm
	share/html/Elements/CollectionList
	share/html/m/_elements/login
        Restored a missing </form> tag made obvious by the merge conflict