REGTESTS: http-rules: test replace-uri and the header replacement actions

REGTESTS: http-rules: test replace-uri and the header replacement actions

replace-uri had no coverage at all, and replace-header and replace-value
were only used by a test checking their size limits, not their
semantics.

The test rewrites a request target in the origin form and in the
absolute form to show that replace-uri also sees the scheme and the
authority, rewrites the scheme of an absolute URI, checks that a non
matching regex leaves the target untouched, and compares the result with
replace-path and replace-pathq on the same target.

It also checks that replace-header replaces the whole header line while
replace-value only replaces the matching comma-delimited element, and
that back-references work in the replacement format.