Update to 9.3.

Update to 9.3.
Use USE_LIBTOOL instead of USE_PKGLIBTOOL.
Changes since 9.2:
o pnmfile: check for file size error.
o ppmhist: handle larger maxvals, image sizes
o xwdtopnm: Use color map with DirectColor to fix wrong color bug on
  some DirectColor xwds.
o xwdtopnm: Correct bug with 24/32 DirectColor LSBfirst xwds.
o Add pXmcheck() library function.
o Add leaftoppm and ppmtoleaf.  Thanks Bill O'Donnell.
o Add winicontoppm and ppmtowinicon.  Thanks Lee Benfield.
o Add pgmslice.  Thanks to Jos Dingjan.
o Include subset of RLE library in the package.
o stamp-date doesn't rely on whoami.
o Make file fixes to accomodate more install programs.
o Replace tmpnam() with mkstemp().
o Add pXm_init() into all programs that didn't have it.