Add -k flag so that curl behavior matches that of wget.
Also, make win32 and unix code more similar (we're almost to the point where we could have a single implementation for both!)
Merge branch 'master' of https://github.com/keplerproject/luarocks

Conflicts:
	src/luarocks/fs/unix/tools.lua
	src/luarocks/fs/win32/tools.lua
Set timeout in LuaSocket/LuaSec based implementation as well.
Be more forgiving with thi cfg.connection_timeout setting.
Add --timeout flag, as discussed in #249.