Refactored Boost Jam's internal yyline() Jamfile parsing function a bit so it no longer uses one unneeded goto that was making the code much harder to read.

[SVN r48533]

tools/build

@@ -1 +1 @@
-Subproject commit 0c0955ab0ab6204e49146a24191231396392d12b
+Subproject commit 42280c7a0f25834eab71f833039fa014cd45b97d