for bug 112708, add an #include so this can be compiled by prefapi.cpp

sr=dveditz, r=bnesse

modules/libpref/src/prefapi_private_data.h

@@ -76,6 +76,7 @@ NSPR_END_EXTERN_C
 
 /* Possibly exportable */
 #if defined(__cplusplus)
+#include "nsIFileSpec.h"
 PrefResult PREF_SavePrefFileSpecWith(
 	nsIFileSpec* fileSpec,
 	PLHashEnumerator heSaveProc);