#12 Add support for a new InnoSetup Preprocessor 'predefined variables'

[José GONÇALVES]

It should be great to add support in InnoSetup Preprocessor for a new 'predefined variables':
. 'WINDOWSVERSION' as a 'str' or an 'int'
and/or new InnoSetup Preprocessor functions:
. GetWindowsVersion(void)
. GetWindowsVersionEx(...)

So, it will be easier and cleaner to do such things (ugly atm):

#if GetEnv("PROCESSOR_ARCHITECTURE") == "x86"
  #define WinXP
...
#elif GetEnv("PROCESSOR_ARCHITECTURE") == "AMD64"
  #define Win7
#endif