Upgrade from libcurl 7.15.5 (2006-08-07) to 7.35.0 (2014-01-29)

Note: This uses the generic curlbuild.h because it is used by multiple platforms.
A system curl would have a configure generated one.

The libraries for win32 and win64 were cross compiled with these options:

  --disable-shared --enable-static --disable-ares --enable-http \
  --enable-ftp --disable-ldap --disable-ldaps --disable-rtsp \
  --disable-dict --disable-file --disable-telnet --disable-tftp \
  --disable-pop3 --disable-imap --disable-smtp --disable-gopher \
  --enable-ipv6 --without-ssl \
  --disable-manual --disable-libcurl-option

This effectively enables only HTTP and FTP protocol support.
Merge branch 'master' into features/upgrade-curl-7.35.0
Fix sending pk3 download error messages to clients

Disabled in e52a492f615e1245d6d22a84d2cc100c6d2f9f88.
Merge pull request #45 from xhairball/features/upgrade-curl-7.35.0

Upgrade libcurl to the latest release (7.35.0).
OpenGL2: Set RGBM to use a multiplier of 1, and only use it with HDR lightmaps.
Merge branch 'master' into fixes/clang-3.4-makefile-support
Don't use -mwindows with Clang on Windows

Thanks to stigmha for pointing out this doesn't work in Windows.