Added new platform commands:

platform connect <args>
platform disconnect

Each platform can decide the args they want to use for "platform connect". I 
will need to add a function that gets the connect options for the current
platform as each one can have different options and argument counts.

Hooked up more functionality in the PlatformMacOSX and PlatformRemoteiOS.
Also started an platform agnostic PlatformRemoteGDBServer.cpp which can end
up being used by one or more actual platforms. It can also be specialized and
allow for platform specific commands.

llvm-svn: 128123