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
Fix remote resources download while hosting SSL site on Apache

As reported by Christian Folin and Walter Hop on our dev mailing list, Apache
mod_ssl was failing if a remote resource was utilized. That was happening
because Curl clean up was also cleaning up the OpenSSL data used by mod_ssl.
This patch moves Curl initialization to happens while ModSecurity is
initialized.
Checks HTTP code after performing a resource download

As reported by Walter Hop on our dev- mailing list, remote resource download
was not validating the HTTP code, parsing errors pages as resources. This
commit fix  this issue, from now one HTTP error codes will be verified and
treated as errors. Operators are now dealing well with empty values that may
be produced in consequence of a download error.
Refactoring external resources download warn messages

Holding the message to be displayed when Apache is ready to write on the
error_log instead of the default output. Regression tests were added.
Adds missing 'ModSecurity:' prefix to log messages

As reported by Walter Hop, the status call functionality was printing a message
in the console without the expected 'ModSecurity:' prefix. SecServerSignature
was also printing messages without the expected prefix. Both are fixed by this
commit.
Informs problems and successfully loaded external resources during reload

Resources load mechanism as the SecRemoteRuels were not showing information
about the loaded rules while Apache was reloaded. This patch add such
information to reload in the same way that it was showing on restart.
Fix typo on fuzzy hash match message

Replaced "Socore" with Score.
Reducing the amount of compilation warnings