[obsolete api] improve deprecation warnings

gnucash/report/report-system/commodity-utilities.scm

@@ -94,7 +94,8 @@
 
 ;; Helper for warnings below.
 (define (gnc-commodity-numeric->string commodity numeric)
-  (issue-deprecation-warning "gnc-commodity-numeric->string deprecated.")
+  (issue-deprecation-warning "gnc-commodity-numeric->string deprecated. \
+construct with gnc:make-gnc-monetary and gnc:monetary->string instead.")
   (gnc:monetary->string
    (gnc:make-gnc-monetary commodity numeric)))
 

gnucash/report/report-system/report-utilities.scm

@@ -38,7 +38,8 @@
 ;; pair is a list of one gnc:commodity and one gnc:numeric
 ;; value. Deprecated -- use <gnc-monetary> instead.
 (define (gnc-commodity-value->string pair)
-  (issue-deprecation-warning "gnc-commodity-value->string deprecated")
+  (issue-deprecation-warning "gnc-commodity-value->string deprecated. \
+construct gnc:make-gnc-monetary and use gnc:monetary->string instead.")
   (xaccPrintAmount
    (cadr pair) (gnc-commodity-print-info (car pair) #t)))