refactor the code that calls validate_against_ca into an helper function to reuse it in both apply_require_ca and (optionally) in apply_reverse_proxy.

printf: Illegal option -i this is why we can't have nice things, isn't it?

While here, move the SRCS variable to the configure and add the -includes in Makefile.local; it de-clutters the Makefile a bit.

as a side effect the order of the content of a server block is relaxed: options, location or proxy blocks can be put in any order.