win32 resource: allow custom comments field in DLL

src/win32/git2.rc

@@ -5,6 +5,10 @@
 # define LIBGIT2_FILENAME "git2"
 #endif
 
+#ifndef LIBGIT2_COMMENTS
+# define LIBGIT2_COMMENTS "For more information visit http://libgit2.github.com/"
+#endif
+
 VS_VERSION_INFO		VERSIONINFO	MOVEABLE IMPURE LOADONCALL DISCARDABLE
   FILEVERSION		LIBGIT2_VER_MAJOR,LIBGIT2_VER_MINOR,LIBGIT2_VER_REVISION,LIBGIT2_VER_PATCH
   PRODUCTVERSION	LIBGIT2_VER_MAJOR,LIBGIT2_VER_MINOR,LIBGIT2_VER_REVISION,LIBGIT2_VER_PATCH
@@ -30,7 +34,7 @@ BEGIN
       VALUE "OriginalFilename",	LIBGIT2_FILENAME ".dll\0"
       VALUE "ProductName",	"libgit2\0"
       VALUE "ProductVersion",	LIBGIT2_VERSION "\0"
-      VALUE "Comments",		"For more information visit http://libgit2.github.com/\0"
+      VALUE "Comments",		LIBGIT2_COMMENTS "\0"
     END
   END
   BLOCK "VarFileInfo"