Point to where the headers are really installed.

--- a/oauth.prf
+++ b/oauth.prf
@@ -1,9 +1,6 @@
-QOAUTH_INCDIR = $$[QT_INSTALL_HEADERS]
+QOAUTH_INCDIR = $$[QT_INSTALL_HEADERS]/..
 QOAUTH_LIBDIR = $$[QT_INSTALL_LIBS]
 
-QOAUTH_INCDIR ~= s!/qt4*!!
-QOAUTH_LIBDIR ~= s!/qt4*!!
-
 CONFIG *= qt
 CONFIG += crypto