[ptx] Compiling VIGRA with MinGW and MSYS

[Yili Zhao]

Hi,
  I want to do some test with nona. Because it uses impex library of VIGRA to load and save images, so I first come to compile VIGRA with MinGW and MSYS.
  I first compile libz, libpng, libtiff and libjpeg, then compile VIGRA and its examples without problem. However, when I invoke its examples (convert.exe, smooth.exe, resize.exe etc.), they all fail with message "precondition violation" when trying to read images. 
  I then recompile VIGRA without linking any image library, and make impex library only suppor built-in image formats. However, when executing these examples, I obtain the same error message.  
  Pablo, you also have MinGW and MSYS environment installed, do you have meet this scenario?
  By the way, I try to compile VIGRA with Cygwin, and every thing goes well. But it seems that applications made by Cygwin can not run indenpentdently without Cygwin evnrionment (need some DLLs of Cygwin).  

Regards
Yili