* plugins/excel/Makefile.am (excel_la_SOURCES): Add crypt-md4.[ch]

* plugins/excel/ms-excel-write.c:
(blipinf_new): New function. Initialize a record for image data.
(blipinf_free): New function. Free an image data record.
(excel_write_image): New function. Write an image Sp record
referencing a BLIP.
(excel_write_objs): Include images in record length. Write images.
(excel_sheet_new): Save image info.
(excel_write_image_bytes): New function. Save image in chunks,
letting the biff layer insert CONTINUE records.
(excel_write_vector_blip): New function. Save a vector format BLIP.
(excel_write_raster_blip): New function. Save a raster format BLIP.
(get_bliptype): New function. Get bliptype record.
(excel_write_blip): New function. Save an image BLIP.
(excel_write_blips): New function. Save the images as BLIPs.
(excel_write_workbook): Get length of BLIP records. Call
excel_write_blips.
(excel_write_state_new): Initialize cur_blip.
(excel_write_state_free): Free BLIP lists from sheets.

* ms-excel-write.h (struct ExcelWriteSheet): Add blips, num_blips.
(struct _ExcelWriteState): Add cur_blip.

* src/sheet-object-image.c (sheet_object_image_new): strdup the
image type.
(sheet_object_image_finalize): Free the image type.
(soi_info_cb): New callback used to find image type.
(soi_get_pixbuf): Install callback on pixbuf loader in order to
find image type.
(sheet_object_image_get_property): New gobject method to return
type, data or pixbuf as object parameters.
(sheet_object_image_class_init): Install properties.