patch 8.1.2001: some source files are too big

Problem:    Some source files are too big.
Solution:   Move buffer and window related functions to evalbuffer.c and
            evalwindow.c. (Yegappan Lakshmanan, closes #4898)
diff --git a/src/Make_mvc.mak b/src/Make_mvc.mak
index 31970fa..0401902 100644
--- a/src/Make_mvc.mak
+++ b/src/Make_mvc.mak
@@ -728,8 +728,10 @@
 	$(OUTDIR)\digraph.obj \
 	$(OUTDIR)\edit.obj \
 	$(OUTDIR)\eval.obj \
+	$(OUTDIR)\evalbuffer.obj \
 	$(OUTDIR)\evalfunc.obj \
 	$(OUTDIR)\evalvars.obj \
+	$(OUTDIR)\evalwindow.obj \
 	$(OUTDIR)\ex_cmds.obj \
 	$(OUTDIR)\ex_cmds2.obj \
 	$(OUTDIR)\ex_docmd.obj \
@@ -1485,10 +1487,14 @@
 
 $(OUTDIR)/eval.obj:	$(OUTDIR) eval.c  $(INCL)
 
+$(OUTDIR)/evalbuffer.obj:	$(OUTDIR) evalbuffer.c  $(INCL)
+
 $(OUTDIR)/evalfunc.obj:	$(OUTDIR) evalfunc.c  $(INCL)
 
 $(OUTDIR)/evalvars.obj:	$(OUTDIR) evalvars.c  $(INCL)
 
+$(OUTDIR)/evalwindow.obj:	$(OUTDIR) evalwindow.c  $(INCL)
+
 $(OUTDIR)/ex_cmds.obj:	$(OUTDIR) ex_cmds.c  $(INCL)
 
 $(OUTDIR)/ex_cmds2.obj:	$(OUTDIR) ex_cmds2.c  $(INCL)
@@ -1775,8 +1781,10 @@
 	proto/digraph.pro \
 	proto/edit.pro \
 	proto/eval.pro \
+	proto/evalbuffer.pro \
 	proto/evalfunc.pro \
 	proto/evalvars.pro \
+	proto/evalwindow.pro \
 	proto/ex_cmds.pro \
 	proto/ex_cmds2.pro \
 	proto/ex_docmd.pro \