Fix build failure introduced by r19285 on systems with guile 1.6.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@19289 57a11ea4-9604-0410-9ed3-97b8803252fd

src/report/report-system/report-system.i

@@ -3,6 +3,7 @@
 /* Includes the header in the wrapper code */
 #include <config.h>
 #include <gnc-report.h>
+#include <guile-mappings.h>
 
 SCM scm_init_sw_report_system_module (void);
 %}