fix issue with sometimes wrong return code of ProcessLogger


As a result of wrong return code Beremiz gives folowing traceback:
Traceback (most recent call last):
File "./Beremiz.py", line 850, in OnMenu
getattr(self.CTR, method)()
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 925, in _Build
IECGenRes = self._Generate_SoftPLC()
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 568, in _Generate_SoftPLC
return self._Compile_ST_to_SoftPLC()
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 661, in _Compile_ST_to_SoftPLC
C_files.remove("POUS.c")
ValueError: list.remove(x): x not in list

The problem is that both threads (for reading stdout and stderr) call self.Proc.poll(),
that updates internal returncode field. This call is done without any locking and the first thread gets correct result,
but other gets 0 as retval. If 0 gets thread, that afterwards calls callback finish, then wrong return code is returned
to the parent. Now only the thread with a callback polls for the return code, other thread just checked local value.

Additionally function spin() waits now until all threads finish reading their pipes, so the results are always correct.

"""
Misc definitions
"""

import os,sys

# helper func to check path write permission
def CheckPathPerm(path):
    if path is None or not os.path.isdir(path):
        return False
    for root, dirs, files in os.walk(path):
         for name in files:
             if os.access(root, os.W_OK) is not True or os.access(os.path.join(root, name), os.W_OK) is not True:
                 return False
    return True

def GetClassImporter(classpath):
    if type(classpath)==str:
        def fac():
            mod=__import__(classpath.rsplit('.',1)[0])
            return reduce(getattr, classpath.split('.')[1:], mod)
        return fac
    else:
        return classpath

def InstallLocalRessources(CWD):
    from BitmapLibrary import AddBitmapFolder
    from TranslationCatalogs import AddCatalog
    import wx

    # Beremiz bitmaps
    AddBitmapFolder(os.path.join(CWD, "images"))

    # Internationalization
    AddCatalog(os.path.join(CWD, "locale"))
    import gettext
    import __builtin__
    
    __builtin__.__dict__['_'] = wx.GetTranslation