Change snd_dlopen() function to return the error string

The dlopen() function might fail also for another reason than
a missing file, thus return the error string from dlerror().

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

src/Versions.in

@@ -129,3 +129,8 @@ ALSA_0.9.7 {
     @SYMBOL_PREFIX@alsa_lisp_*;
 } ALSA_0.9.5;
 
+ALSA_1.1.6 {
+  global:
+
+    @SYMBOL_PREFIX@snd_dlopen;
+} ALSA_0.9.7;