core: add missing declaration of "environ" (fix compilation on Mac OS X)

src/core/wee-command.c

@@ -78,6 +78,9 @@
 #include "../plugins/plugin-config.h"
 
 
+extern char **environ;
+
+
 /*
  * Callback for command "/away".
  *

src/core/wee-completion.c

@@ -55,6 +55,9 @@
 #include "../plugins/plugin.h"
 
 
+extern char **environ;
+
+
 /*
  * Adds bar names to completion list.
  */