It is possible that some arguments within the configuration line are not
specified; that is, they are set to a blank string.
For example:
keyword '' arg_2
In that case the content of the args field will be like this:
args[0]: 'keyword'
args[1]: NULL pointer
args[2]: 'arg_2'
args[3 .. MAX_LINE_ARGS): NULL pointers
The previous way of calculating the number of arguments (as soon as a
null pointer is encountered) could not place an argument on an empty
string.
All of the above is essential for passing the OpenTracing context via
the HTTP headers (keyword 'inject'), where one of the arguments is the
context name prefix. This way we can set an empty prefix, which is very
useful if we get context from some other process that can't add a prefix
to that data; or we want to pass the context to some process that cannot
handle the prefix of that data.
This one is the last optional module to build with haproxy, so let's move
it to addons/. It was renamed to "ot" as it was the only one whose USE_*
option did not match the directory name, now this is consistent.
Few changes were required, only the Makefile, and doc were adjusted, as
the directory was already self-contained and relocatable.
