building.py: append messed up objs list, use extend to avoid that

The return type of SConscript is a subclass of UserList. We should use
extend to keep the depth of the list is always 1 when concatenate
SConscript return values. Thanks prife for making me realize that this
is really a problem.

Reported-and-Tested-by: prife
Merge pull request #37 from grissiom/fix-building-py

building.py: append messed up objs list, use extend to avoid that
basic mingw support for simulator: kernel and finsh
mingw support for simulator: dfs/fatfs
mingw support for simulator: dfs/dfs_win32
mingw support for simulator: dfs/uffs
mingw support for simulator: rtgui
app module support for simlator, first version
Merge branch 'master' of github.com:RT-Thread/rt-thread into sim-module
app module of simlator: rename librtthread.a to rtthread.lib after post-building
app module of simlator: simpliy command of building, now use `scons --def` to create rtthread.def which can used by msvc
app module simulator: add app module test cases
Merge pull request #39 from prife/sim-module

simulator: mingw and  app module support