This macro should be used to declare variables or struct members depending on
the USE_THREAD compile option. It avoids the encapsulation of such declarations
between #ifdef/#endif. It is used to declare all lock variables.
A RW lock has been added to the vars structure to protect each list of
variables. And a global RW lock is used to protect registered names.
When a varibable is fetched, we duplicate sample data because the variable could
be modified by another thread.
Now it is possible to use variables attached to a process. The scope name is
'proc'. These variables are released only when HAProxy is stopped.
'tune.vars.proc-max-size' directive has been added to confiure the maximum
amount of memory used by "proc" variables. And because memory accounting is
hierachical for variables, memory for "proc" vars includes memory for "sess"
vars.
This patch adds support of variables during the processing of each stream. The
variables scope can be set as 'session', 'transaction', 'request' or 'response'.
The variable type is the type returned by the assignment expression. The type
can change while the processing.
The allocated memory can be controlled for each scope and each request, and for
the global process.
