MEDIUM: regex: Remove null terminated strings.

MEDIUM: regex: Remove null terminated strings.

The new regex function can use string and length. The HAproxy buffer are
not null-terminated, and the use of the regex_exec* functions implies
the add of this null character. This patch replace these function by the
functions which takes a string and length as input.

Just the file "proto_http.c" is change because this one is more executed
than other. The file "checks.c" have a very low usage, and it is not
interesting to change it. Furthermore, the buffer used by "checks.c" are
null-terminated.