bug#7955: patch for imagemagick header rename

[Glenn Morris <rgm@gnu.org>]

Seems fine on RHEL5. On RHEL4, build still fails.

configure says:

checking IMAGEMAGICK_CFLAGS...  
checking IMAGEMAGICK_LIBS... -lWand -lMagick  
checking for MagickExportImagePixels... no
checking wand/MagickWand.h usability... no
checking wand/MagickWand.h presence... no
checking for wand/MagickWand.h... no
  Does Emacs use imagemagick?                             yes

make says:

image.c: In function `imagemagick_load_image':
image.c:7521: warning: implicit declaration of function `MagickWandGenesis'
image.c:7525: warning: implicit declaration of function `MagickSetResolution'
image.c:7532: warning: implicit declaration of function `MagickPingImageBlob'
image.c:7560: warning: implicit declaration of function `AcquireExceptionInfo'
image.c:7560: warning: assignment makes pointer from integer without a cast
image.c:7725: warning: implicit declaration of function `PixelGetMagickColor'
image.c:7809: warning: implicit declaration of function `MagickWandTerminus'
image.c: In function `Fimagemagick_types':
image.c:7899: error: too many arguments to function `GetMagickList'
make[1]: *** [image.o] Error 1

/usr/include/magick/magick.h says:

 **GetMagickList(const char *,unsigned long *),


Looks like it may be best for configure to check for a minimum
imagemagick version.