Squashed 'libs/libhtp/' changes from 9ff8285..fa3d9c3

fa3d9c3 Do not allow content handlers to be invoked after the final invocation.
fa8b0d1 Check that the API is rejecting NULL request and response body data in hybrid mode.
56d4ec5 Remove bogus regression tests.
fd0ef70 Do not allow response body pointers to be NULL. Improve validation of many functions, not allowing NULLs where appropriate. Improve documentation.

git-subtree-dir: libs/libhtp
git-subtree-split: fa3d9c3f3b0f1195cdeb875f9bd90dccb3cabc43
Merge commit '61dd1b57cd7396e7cabaa2856f7694913e5396da' (LibHTP) into 0.7.x
'body data with no data' messages now log w/tx
Backporting Lua Stack changes. A new Lua stack is created for each connection.
Remove whitespace.
Tightening constraints on ironbee.
Adding more debugging.
Copy file names into reloading list.
Doxygen fix.
Trafficserver: Removed connection open hook
Fixing possible memory leak reported by clan-3.2-scan-build.
modhtp: Always inform LibHTP of request body
Fixing bug where strings are implicitly converted to numbers (and fail).
rule_set_chain -> ib_rule_set_chain in ironbee/config.lua.
Do not do directive configuration if there is no directive registration function.