New mod chooser preview image for Red Alert
Merge pull request #5518 from obrakmann/ra-preview-img

closes #5333
try to debug what is going on with $TRAVIS_TAG
Merge pull request #5519 from Mailaender/travis-deploy-debug

Try to debug what is going on with $TRAVIS_TAG
fix the Travis deployment
was useful, but is kinda spammy
Merge pull request #5521 from Mailaender/travis-tagged-branches-errr-whatever

Fixed $TRAVIS_TAG being empty on release branches
Make RenderSprites aware of EffectiveOwner. Fixes #5526.
Merge pull request #5527 from pchote/spy-fix

Make RenderSprites aware of EffectiveOwner.
avoid InvalidOperation and NullReferenceException

fixes #5522
fix a rare NullReferenceException in CanUnload

closes #5528
Merge pull request #5529 from Mailaender/rare-pillbox-nre

Fixed a rare NullReferenceException in CanUnload
Merge pull request #5523 from Mailaender/dead-repair-indicator

avoid InvalidOperation and NullReferenceException
Remove incriminating evidence from the RA preview image

Addresses Scott's concern about the wrong explosion type on the sub pen.
Fix issues in 'intervention' mission

* Fix an InvalidOperationException due to querying traits on a dead
  actor (fixes #5530)
* remove a gap in the SAM belt that shouldn't be there
Merge pull request #5532 from obrakmann/random-fixes

Random fixes
Slackware 13.37 is way too old for us now
update Debian/Ubuntu and SUSE build dependencies
document Lua 5.1 for Windows
fixed syntax errors