Fixed: crash trying to 'test_write' on Windows (Image3.rb, ImageList2.rb)

### Error message

No error message and no finish message as follows
```
C:\ruby\Ruby200-x64\lib\ruby\gems\2.0.0\gems\rmagick-2.13.3\test>ruby test_all_basic.rb
C:/ruby/Ruby200-x64/lib/ruby/site_ruby/2.0.0/RMagick.rb:1836: warning: assigned but unused variable - current
2.0.0
String
C:/ruby/Ruby200-x64/lib/ruby/gems/2.0.0/gems/rmagick-2.13.3/test/Image3.rb:653: warning: assigned but unused variable -
img
Loaded suite test_all_basic
Started
.........................................................................
C:\ruby\Ruby200-x64\lib\ruby\gems\2.0.0\gems\rmagick-2.13.3\test>
```

### Cause
C Runtime libraries version incompatibility

Ruby
![ruby200_](https://cloud.githubusercontent.com/assets/6265511/4046347/88895798-2d31-11e4-941d-7ead046e6d64.png)

ImageMagick
![magick_](https://cloud.githubusercontent.com/assets/6265511/4046338/7d490a40-2d31-11e4-99e5-c0819fc6b843.png)

<a href="https://www.ruby-forum.com/topic/70810#96932">Win32 Extension Issues Wanted! - Ruby Forum</a>

(1) On Ruby(*msvcrt.dll*)
(2) On RMagick2.so(*msvcrt.dll*)
(3) On ImageMagick(*msvcr100.dll*)

(1) <-> (2) pass
(2) <-> (3) fail

Therefore, I fixed RMagick so that a file is opened on ImageMagick.