Makes Curl no longer a mandatory depedency for ModSecurity core

As reported by Rainer Jung, Curl may not be mandatory to build
	ModSecurity core. This patch make it optional by:
	- Concentrate all downloads using curl on msc_remote_rules.c
	- Split Curl build definitions checks into: WITH_CURL, WITH_REMOTE_RULES
	and WITH_CRYPTO.
	  - WITH_CURL: Contains Culr headers and binaries during the build time.
	  - WITH_REMOTE_RULES: Currently enabled if Curl is present.
	  - WITH_CRYPTO: Set if apr tool was compiled with crypto support.
	- Renames msc_remote_grab_content to msc_remote_download_content

tests/Makefile.am

@@ -6,6 +6,7 @@ msc_test_SOURCES = msc_test.c \
     ../apache2/libinjection/libinjection_xss.c \
     ../apache2/modsecurity.c \
     ../apache2/msc_status_engine.c \
+    ../apache2/msc_remote_rules.c \
     ../apache2/msc_crypt.c \
     ../apache2/msc_geo.c \
     ../apache2/msc_gsb.c \
@@ -28,7 +29,8 @@ msc_test_SOURCES = msc_test.c \
     ../apache2/re_tfns.c \
     ../apache2/re_variables.c \
     ../standalone/regex.c \
-    ../standalone/server.c
+    ../standalone/server.c \
+    ../standalone/config.c
 
 msc_test_CFLAGS = @APR_CFLAGS@ \
     @APU_CFLAGS@ \

tests/msc_test.c

@@ -79,6 +79,15 @@ unsigned long int DSOLOCAL msc_pcre_match_limit = 0;
 unsigned long int DSOLOCAL msc_pcre_match_limit_recursion = 0;
 char DSOLOCAL *real_server_signature = NULL;
 int DSOLOCAL remote_rules_fail_action = REMOTE_RULES_ABORT_ON_FAIL;
+module AP_MODULE_DECLARE_DATA security2_module = {
+    NULL,
+    NULL,
+    NULL,
+    NULL,
+    NULL,
+    NULL,
+    NULL
+};
 
 /* Stubs */
 char *format_error_log_message(apr_pool_t *mp, error_message_t *em) {