Squashed 'libs/libhtp/' changes from 2134d03..236bcfe

236bcfe Improve error logging.
71f29e6 Fix memory leak.
ef57848 Fix memory leak and tidy up.
96d985e Fix double Content-Length issue.

git-subtree-dir: libs/libhtp
git-subtree-split: 236bcfe1282ed996ae7e357524e464bb754afcac
libhtp: Merge with upstream 0.5.x.