proxy.c now no longer refers to `cfg'. Instead, each of the three

proxy.c now no longer refers to `cfg'. Instead, each of the three
proxy-indirection network functions (name_lookup, new_connection,
new_listener) takes a `const Config *' as an argument, and extracts
enough information from it before returning to handle that
particular network operation in accordance with the proxy settings
it specifies. This involved {win,ux}net.c due to a `const'
repercussion.

git-svn-id: svn://svn.tartarus.org/sgt/putty@2567 cda61777-01e9-0310-a592-d414129be87e