Adding http_free_redirect_rule() function to free a single redirect rule
since it may be required to free rules outside of free_proxy() function.

This patch is required for an upcoming bugfix.

[for 2.2, free_proxy function did not exist (first seen in 2.4), thus
http_free_redirect_rule() needs to be deducted from haproxy.c deinit()
function if the patch is required]

The 3 functions http_{req,res,after_res}_keywords_register() are
referenced in initcalls by their pointer, it makes no sense to declare
them inline. At best it causes function duplication, at worst it doesn't
build on older compilers.

The current "ADD" vs "ADDQ" is confusing because when thinking in terms
of appending at the end of a list, "ADD" naturally comes to mind, but
here it does the opposite, it inserts. Several times already it's been
incorrectly used where ADDQ was expected, the latest of which was a
fortunate accident explained in 6fa922562 ("CLEANUP: stream: explain
why we queue the stream at the head of the server list").

Let's use more explicit (but slightly longer) names now:

   LIST_ADD        ->       LIST_INSERT
   LIST_ADDQ       ->       LIST_APPEND
   LIST_ADDED      ->       LIST_INLIST
   LIST_DEL        ->       LIST_DELETE

The same is true for MT_LISTs, including their "TRY" variant.
LIST_DEL_INIT keeps its short name to encourage to use it instead of the
lazier LIST_DELETE which is often less safe.

The change is large (~674 non-comment entries) but is mechanical enough
to remain safe. No permutation was performed, so any out-of-tree code
can easily map older names to new ones.

The list doc was updated.

These functions will be useful to check if a keyword is already registered.
This will be needed by a next patch to fix a bug, and will need to be
backported.

This patch fixes all the leftovers from the include cleanup campaign. There
were not that many (~400 entries in ~150 files) but it was definitely worth
doing it as it revealed a few duplicates.

This one is particularly difficult to split because it provides all the
functions used to manipulate a proxy state and to retrieve names or IDs
for error reporting, and as such, it was included in 73 files (down to
68 after cleanup). It would deserve a small cleanup though the cut points
are not obvious at the moment given the number of structs involved in
the struct proxy itself.

There was no include file. This one still includes types/proxy.h.