Added definition for the USERINFOSTATE enumeration.

include/msi.h

diff --git a/include/msi.h b/include/msi.h
index c73c9f9..0c8aa57 100644
--- a/include/msi.h
+++ b/include/msi.h
@@ -55,6 +55,15 @@
     INSTALLUILEVEL_SOURCERESONLY = 0x100
 } INSTALLUILEVEL;
 
+typedef enum tagUSERINFOSTATE
+{
+    USERINFOSTATE_MOREDATA = -3,
+    USERINFOSTATE_INVALIDARG = -2,
+    USERINFOSTATE_UNKNOWN = -1,
+    USERINFOSTATE_ABSENT = 0,
+    USERINFOSTATE_PRESENT = 1,
+} USERINFOSTATE;
+
 typedef enum tagINSTALLLEVEL
 {
     INSTALLLEVEL_DEFAULT = 0,