MINOR: acl: add extra diagnostics about suspicious string patterns

MINOR: acl: add extra diagnostics about suspicious string patterns

As noticed in this thread, some bogus configurations are not always easy
to spot: https://www.mail-archive.com/haproxy@formilux.org/msg44558.html
Here it was about config keywords being used in ACL patterns where strings
were expected, hence they're always valid.

Since we have the diag mode (-dD) we can perform some extra checks when
it's used, and emit them to suggest the user there might be an issue.

Here we detect a few common words (logic such as "and"/"or"/"||" etc),
C++/JS comments mistakenly used to try to isolate final args, and words
that have the exact name of a sample fetch or an ACL keyword. These checks
are only done in diag mode of course.