2015-10-12: resolve wisp source in backtrace bug (partially resolved, noted as

resolve wisp source in backtrace bug (partially resolved, noted as limitation)

diff --git a/.bugs/bugs b/.bugs/bugs
--- a/.bugs/bugs
+++ b/.bugs/bugs
@@ -1,5 +1,5 @@
 testsuite: to pass, the tree-il has to match, not the emitted string. This allows for reader-only implementations. | owner:, open:False, id:00b74a730bbf076e73166e817ca7b0a273b376d4, time:1408224636.42
-wisp-scheme: backtraces should show the wisp source.         | owner:Arne Babenhauserheide <bab@draketo.de>, open:True, id:0475df81a594a52d171a1b811752ca64e5a71df5, time:1426792099.58
+wisp-scheme: backtraces should show the wisp source.         | owner:Arne Babenhauserheide <bab@draketo.de>, open:False, id:0475df81a594a52d171a1b811752ca64e5a71df5, time:1426792099.58
 wisp-scheme: unescape \_ and \:                              | owner:, open:False, id:086f61a06e16f1ef56e9917453bbd55b5879d15d, time:1415121255.99
 fails when I add stuff at the end of end of example.w        | owner:, open:False, id:08c68e1ce0c9798184c01806d2661a3220bff3cd, time:1363789693.79
 wisp-mode in quoted lists only the first item is colorized as data, but all words up to the last paren should be colorized. | owner:, open:True, id:1675ca3f894ed8470fa292149a476a2fa0d17140, time:1397196957.45
diff --git a/wisp-scheme.w b/wisp-scheme.w
--- a/wisp-scheme.w
+++ b/wisp-scheme.w
@@ -9,6 +9,8 @@ exec guile -L . --language=wisp -s "$0" 
 
 ;; Limitations:
 ;; - only unescapes up to 6 leading underscores at line start (\______)
+;; - in some cases the source line information is missing in backtraces.
+;;   check for set-source-property!
 
 ;; Copyright (C) Arne Babenhauserheide (2014--2015). All Rights Reserved.