Move all defaulting-of-CAP_FOO to sysconfig.h.

- The phrase `#ifdef CAP_` should never appear anywhere.

- The phrase `#ifndef CAP_` should appear only in sysconfig.h.

- The phrases `#if CAP_` and `#if !CAP_` may appear wherever,
    as long as "sysconfig.h" is included first.

The rules for `CAP_FOO` equally apply to `ISFOO`.

There are many one-off macros still tested with `#ifdef`,
including `HAVE_ACHIEVEMENTS`, `PRINT_ACHIEVEMENTS`,
`FAKEWEB`, `FAKE_SDL`, `EASY`, and `WHATEVER`. I don't
have much grasp on what these are used for or how they're
configured, so I'm leaving them alone.

multi.cpp

@@ -549,7 +549,7 @@ EX void initConfig() {
   t[(int)'s'] = 16 + 6;
   t[(int)'a'] = 16 + 7;
 
-#if ISMOBILE==0
+#if !ISMOBILE
   t[SDLK_KP8] = 16 + 4;
   t[SDLK_KP6] = 16 + 5;
   t[SDLK_KP2] = 16 + 6;
@@ -572,7 +572,7 @@ EX void initConfig() {
   t[(int)'p'] = 32 + 10;
   t[(int)'['] = 32 + pcCenter;
 
-#if ISMOBILE==0
+#if !ISMOBILE
   t[SDLK_UP] = 48 ;
   t[SDLK_RIGHT] = 48 + 1;
   t[SDLK_DOWN] = 48 + 2;
@@ -973,4 +973,4 @@ EX void handleInput(int delta) {
   
   EX }
 
-}
+}