1. Change `ai_profile_lookup` and `multi_xfer_lookup` to use `const char *`, since all the other lookup functions do
2. Remove several unneeded `const_cast`s, some of which are now made possible by the non-const `data()` overload in C++17
3. Change `campaign_link` to use `const char*`
4. Use better string management in `test::FSTestFixture::init_cmdline()`
FSO doesn't appear to use this any longer. And even when it was enabled the
requirements made it largely useless anyway. Removing to clean up cfile a
bit and so we don't have to keep maintaining it.
A bit overkill for some of this but just covering the bases.
* fix issues with in-game join
* fix multi messaging and multi pause screen
* make sure maintenance stuff (pings, voice, file xfer, etc.) isn't
affected by pausing or time compression
make sure NO_NETWORK builds are as friendly on Windows as it is on Linux/OSX
revert a timeout in Client.h back to the original value before Linux merge
Goober5000