writeDepsFile: write included files as well

`writeDepsFile()` does not list files which were included with the
`include` statement, e.g, with:

    import file1
    include file2

`file1` will be written to the deps file, while `file2` would not.

Fix this by modifying `writeDepsFile()` to write included files as well.
Now, both `file1` and `file2` in the above example will be written to
the deps file.

compiler/main.nim

@@ -16,7 +16,7 @@ import
   cgen, jsgen, json, nversion,
   platform, nimconf, importer, passaux, depends, vm, vmdef, types, idgen,
   docgen2, service, parser, modules, ccgutils, sigmatch, ropes,
-  modulegraphs
+  modulegraphs, tables
 
 from magicsys import systemModule, resetSysTypes
 
@@ -36,6 +36,9 @@ proc writeDepsFile(g: ModuleGraph; project: string) =
   for m in g.modules:
     if m != nil:
       f.writeLine(toFullPath(m.position.int32))
+  for k in g.inclToMod.keys:
+    if g.getModule(k).isNil:  # don't repeat includes which are also modules
+      f.writeLine(k.toFullPath)
   f.close()
 
 proc commandGenDepend(graph: ModuleGraph; cache: IdentCache) =