Branch: branches/ruby_1_8

Symptoms: Builds using MingW are failing when building in separate 
directory from source. Attempts to delete miniruby.exe fails with 
permission error.

Cause: version.o + miniruby are always recompiled, even when there is no 
update to revision.h. Attempts to delete rebuild miniruby.exe while 
miniruby.exe is running.

Index: common.mk
===================================================================
--- common.mk   (revision 17575)
+++ common.mk   (working copy)
@@ -471,7 +471,7 @@
 dist: $(PROGRAM)
        $(RUNRUBY) $(srcdir)/distruby.rb

-{$(VPATH)}revision.h: revision.h.tmp
+$(srcdir)/revision.h: revision.h.tmp
        @if [ -f $(srcdir)/revision.h ] && { [ ! -s $? ] || cmp 
$(srcdir)/revision.h $? >/dev/null; }; then \
          $(RM) $?; \
        else \