[devel] Changed some "#if defined(" to "ifdef"

and revised libpng style to mention not using the TAB character.
diff --git a/CHANGES b/CHANGES
index 7f8ddbc..f8b809a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2236,11 +2236,12 @@
     (Dennis Gustafsson)
   Fixed typo introduced in beta78 in pngtest.c ("#if def " should be "#ifdef ") 
 
-version 1.4.0beta81 [September 20, 2009]
+version 1.4.0beta81 [September 23, 2009]
   Eliminated unused PNG_FLAG_FREE_* defines from pngpriv.h
   Expanded TAB characters in pngrtran.c
   Removed PNG_CONST from all "PNG_CONST PNG_CHNK" declarations to avoid
     compiler complaints about doubly declaring things "const".
+  Changed some "#if defined(" to "ifdef"
 
 version 1.4.0betaN [future]
   Build shared libraries with -lz and sometimes -lm.