audio: Support "pulse" as an alias for "pulseaudio"

Originally, SDL 1.2 used "pulse" as the name for its PulseAudio driver.
While it now supports "pulseaudio" as well for compatibility with SDL
2.0 [1], there are still scripts and distro packages which set
SDL_AUDIODRIVER=pulse [2]. While it's possible to remove this in most
circumstances or replace it with "pulseaudio" or a comma-separated list,
this may still conflict if the environment variable is set globally and
old binary builds of SDL 1.2 (e.g. packaged with older games) are being
used.

To fix this on SDL 2.0, add a hardcoded check for "pulse" as an audio
driver name, and replace it with "pulseaudio". This mimics what SDL 1.2
does (but in reverse). Note that setting driver_attempt{,_len} is safe
here as they're reset correctly based on driver_attempt_end on the next
loop.

[1] https://github.com/libsdl-org/SDL-1.2/commit/d9514097846381cd30fe08df65dbdd48de92a058
[2] https://bugzilla.opensuse.org/show_bug.cgi?id=1189778

src/audio/SDL_audio.c

@@ -978,6 +978,14 @@ SDL_AudioInit(const char *driver_name)
             const char *driver_attempt_end = SDL_strchr(driver_attempt, ',');
             size_t driver_attempt_len = (driver_attempt_end != NULL) ? (driver_attempt_end - driver_attempt)
                                                                      : SDL_strlen(driver_attempt);
+#if SDL_AUDIO_DRIVER_PULSEAUDIO
+            /* SDL 1.2 uses the name "pulse", so we'll support both. */
+            if (driver_attempt_len == SDL_strlen("pulse") &&
+                (SDL_strncasecmp(driver_attempt, "pulse", driver_attempt_len) == 0)) {
+                driver_attempt = "pulseaudio";
+                driver_attempt_len = SDL_strlen("pulseaudio");
+            }
+#endif
 
             for (i = 0; bootstrap[i]; ++i) {
                 if ((driver_attempt_len == SDL_strlen(bootstrap[i]->name)) &&