trivial plotutils build errors

[Craig Maloney]

I have not included a patch, as somehow the .cc files are generated
dynamically during the build process from c files and I do not
understand this process.

Building against g++-3.2.1:
Configured with --prefix=~/usr/local --enable-libplotter

make output:
--------------------------------------------
c++ -DHAVE_CONFIG_H -I. -I. -I.. -I/usr/X11R6/include -I./../include
-DLIBPLOT -DLIBPLOTTER -O2 -c g_write.cc  -fPIC -DPIC -o
.libs/g_write.lo
------------------------------------------
g_write.cc: In function `void _write_bytes(const plPlotterData*, int,
const
   unsigned char*)':
g_write.cc:43: invalid conversion from `const unsigned char*' to `const
char*'
g_write.cc:43:   initializing argument 1 of `std::basic_ostream<_CharT,
   _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*,
int)
   [with _CharT = char, _Traits = std::char_traits<char>]'
make[2]: *** [g_write.lo] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all-recursive-am] Error 2
----------------------------------------------

c++ -DHAVE_CONFIG_H -I. -I. -I.. -I/usr/X11R6/include -I./../include
-DLIBPLOT -DLIBPLOTTER -O2 -c i_rle.cc  -fPIC -DPIC -o
.libs/i_rle.lo
------------------------------------------------
i_rle.cc: In function `void _write_block(rle_out*)':
i_rle.cc:81: invalid conversion from `unsigned char*' to `const char*'
i_rle.cc:81:   initializing argument 1 of `std::basic_ostream<_CharT,
_Traits>&
   std::basic_ostream<_CharT, _Traits>::write(const _CharT*, int) [with
_CharT
   = char, _Traits = std::char_traits<char>]'
make[2]: *** [i_rle.lo] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all-recursive-am] Error 2
-------------------------------------------------

n_write.cc: In member function `void PNMPlotter::_n_write_pbm()':
n_write.cc:211: invalid conversion from `unsigned char*' to `const
char*'
n_write.cc:211:   initializing argument 1 of `std::basic_ostream<_CharT,

   _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*,
int)
   [with _CharT = char, _Traits = std::char_traits<char>]'
n_write.cc:256: invalid conversion from `unsigned char*' to `const
char*'
n_write.cc:256:   initializing argument 1 of `std::basic_ostream<_CharT,

   _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*,
int)
   [with _CharT = char, _Traits = std::char_traits<char>]'
n_write.cc: In member function `void PNMPlotter::_n_write_pgm()':
n_write.cc:369: invalid conversion from `unsigned char*' to `const
char*'
n_write.cc:369:   initializing argument 1 of `std::basic_ostream<_CharT,

   _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*,
int)
   [with _CharT = char, _Traits = std::char_traits<char>]'
n_write.cc:395: invalid conversion from `unsigned char*' to `const
char*'
n_write.cc:395:   initializing argument 1 of `std::basic_ostream<_CharT,

   _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*,
int)
   [with _CharT = char, _Traits = std::char_traits<char>]'
n_write.cc: In member function `void PNMPlotter::_n_write_ppm()':
n_write.cc:517: invalid conversion from `unsigned char*' to `const
char*'
n_write.cc:517:   initializing argument 1 of `std::basic_ostream<_CharT,

   _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*,
int)
   [with _CharT = char, _Traits = std::char_traits<char>]'
n_write.cc:545: invalid conversion from `unsigned char*' to `const
char*'
n_write.cc:545:   initializing argument 1 of `std::basic_ostream<_CharT,

   _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*,
int)
   [with _CharT = char, _Traits = std::char_traits<char>]'
make[2]: *** [n_write.lo] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all-recursive-am] Error 2

----------------------------------------------------------

z_write.cc: In function `void _our_write_fn(png_struct*, png_byte*,
unsigned
   int)':
z_write.cc:487: invalid conversion from `png_byte*' to `const char*'
z_write.cc:487:   initializing argument 1 of `std::basic_ostream<_CharT,

   _Traits>& std::basic_ostream<_CharT, _Traits>::write(const _CharT*,
int)
   [with _CharT = char, _Traits = std::char_traits<char>]'
make[2]: *** [z_write.lo] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all-recursive-am] Error 2

---------------------------------------------------------