BUILD: stdbool is not portable (again)

Another build issue on Solaris without c99. Please don't use stdbool.
DOC: readme: add a small reminder about restrictions to respect in the code

For code portability, we need to respect a few restrictions (mainly no C99 etc).
MINOR: ebtree: add new eb_next_dup/eb_prev_dup() functions to visit duplicates

Sometimes it's very useful to visit duplicates of a same node, but doing
so from the application is not convenient because keys have to be compared,
while all the information is available during the next/prev steps.

Let's introduce a couple of new eb_next_dup/eb_prev_dup functions to visit
only duplicates of the current node and return NULL once it's done. Now we
have all 3 combinations :
  - next        : returns next node in the tree
  - next_dup    : returns next dup in the sub-tree
  - next_unique : returns next value after skipping dups

(cherry picked from commit 3327b8ae6866f3878322a1a29e70b450226d216d)
MEDIUM: ssl: improve crt-list format to support negation

Improve the crt-list file format to allow a rule to negate a certain SNI :

        <crtfile> [[!]<snifilter> ...]

This can be useful when a domain supports a wildcard but you don't want to
deliver the wildcard cert for certain specific domains.
BUG/MINOR: acl: fix a double free during exit when using PCRE_JIT

When freeing ACL regex, we don't want to perform the free() in regex_free()
as it's already performed in free_pattern(). The double free only happens
when using PCRE_JIT when freeing everything during exit so it's harmless
but exhibits libc errors during a reload/restart.

Bug reported by Seri.