Add fallback for __func__ (ioq3 isn't compiled as c99 by default)

Using Debian gcc version 4.7.2 and clang 3.0-6.1 anyway.
Remove unused code for in_buttons[15]

button 15 is BUTTON_ANY, auto set if any key is pressed, so don't need client command for setting it.
Merge remote-tracking branch 'ioquake3/master'