builtin curl - especially on Darwin

[Sevan Janiyan <venture37%geeklan.co.uk@localhost>]

Hello,
Some of the operating systems which we support ship with curl out of the
box. As time moves on, older versions of operating systems stop
receiving updates, continuing to use such built in components become
dangerous.
Curl like many other popular software projects has received a fair share
of advisories over the user.

On Tiger, curl --version reports
curl 7.16.3 (powerpc-apple-darwin8.0) libcurl/7.16.3 OpenSSL/0.9.7l
zlib/1.2.3
Protocols: tftp ftp telnet dict ldap http file https ftps
Features: GSS-Negotiate IPv6 Largefile NTLM SSL libz

:)

What's the best way to not utilise outdated version of software such of
curl in mk/tools/tools.$OS.mk.


Sevan