Cleaned up internal ScmWriteContext handling
Merge pull request #20 from rui314/master

Fix bug that :equal parameter is ignored
Changelog for the last commit
Removed duplicate typedef of ScmWriteContext
Fixed a bug that yielded invalid vminsn.c source if there's no source-info

http://chaton.practical-scheme.net/gauche/a/2013/10/15#entry-525ccb4d-6f8b3
Fixed a bug that inadvertently dropped SOURCE_INFO flag by default

The bug was introduced by commit 2470767.
Avoid 'control may reach end of non-void function' warnings
Avoid using tab to indent
Fix build error in out-of-tree build
Untabified source files

Except the sources originated from somewhere else
Fix writer subroutines' return vaules
Document addition
Fix bug that topological-sort did not detect cycle

The previous implementation of cycle detection does not always work because
there's at least one node with no incoming edge does not mean that there's
no cycle in the graph.