Adds real_server_signature symbol to msc_test

Missing symbol was leading the tests to fail
Adds curl support to main core

Curl was used only by mlogc, as we want to expand ModSecurity to load
external rules/resources it is now a dependency of the core as well.
Adds support to load remote resources to pmFromFile and ipMatchFromFile

Initially those directives were only able to load content from a
local file. This commit extends this functionality allowing the user to
provide an HTTP URI that can be downloaded and loaded by ModSecurity.
Initially the download is associated with a server restart. For next
versions we expect to load such resources as it become outdated (Without
need to resetart the server).
Initial support to load rules from a remote server

New directive `SecRemoteRules' was added. It allows the user to load a
set of rules from a given HTTP server.