graphics/ipe: Update patch to support DragonFly

DragonFly 3.4 uses char* prototype for iconv while the upcoming
DragonFly 3.6 uses const char* iconv prototype like FreeBSD does.
Modify the iconv patch to allow graphics/ipe to build on both
DragonFly releases.

graphics/ipe/files/patch-ipelib__ipedoc.cpp

@@ -1,11 +1,23 @@
---- ipelib/ipedoc.cpp.orig
+--- ipelib/ipedoc.cpp.orig	2013-03-15 13:37:02.000000000 +0000
 +++ ipelib/ipedoc.cpp
-@@ -850,7 +850,7 @@
+@@ -41,6 +41,7 @@
+ #include "ipelatex.h"
+ 
+ #include <errno.h>
++#include <sys/param.h>
+ 
+ #ifdef IPE_USE_ICONV
+ #include <iconv.h>
+@@ -850,7 +851,12 @@ int Document::runLatex(String &texLog)
      if (!file)
        return ErrWritingSource;
  
--    char *inbuf = (char *) utf8.data();
++#if defined(__FreeBSD__) || \
++   (defined(__DragonFly__) && __DragonFly_version > 300502)
 +    const char *inbuf = utf8.data();
++#else
+     char *inbuf = (char *) utf8.data();
++#endif
      size_t inbytesleft = utf8.size();
  
      FileStream fstream(file);