curl now with native SSL/TLS on Mac and WNT

hi Cedric,

digging through curl's makefiles it supports some native SSL/TLS
implementations, which should have OS integrated support and UI for
adding custom CAs and such things:

commit 461bdf0b4f863a5ba39dd76b6baf416fbb64b5e8 enables use of "Secure
Transport" on Mac / IOS

commit 460d6ce526b79f4d98600d60a63f894e197b66fe enables use of
"Schannel" on WNT (MSVC)

and btw commit 88e65df2e4be47ae3ae1ae1b3a30003f4cfe4b11
upgrades to version 7.33.0

actually it appears that on WNT our internal curl didn't have any
SSL/TLS support before, which is surprising (but i haven't checked 4.1,
maybe that was only on master).

it appears that Mac OS X 10.6 has a system libcurl.4.dylib, which could
perhaps also be used; our RHEL5 baseline has a libcurl.so.3 apparently
which is too old.

this is build-tested only (and Mac only via tinderbox) - please test if
it actually works for your use-cases.