table, to avoid cpp failure on SunOS (introduced PNG_BUILDING_SYMBOL_TABLE
macro).

This reverts commit 2438825d.

accommodate the old VisualC++ preprocessor.
Defined PNG_ALLOCATED to empty for MSC_VER < 1300.

argument names file_gamma, int_file_gamma, and srgb_intent consistently.

 the namespace.  Added png_get_current_row_number and
 png_get_current_pass_number for the
 benefit of the user transform callback.
 Added png_process_data_pause and png_process_data_skip for the benefit of
 progressive readers that need to stop data processing or want to optimize
 skipping of unread data (e.g. if the reader marks a chunk to be skipped.)

    Added a make macro DFNCPP that is a CPP that will accept the tokens in
    a .dfn file and adds configure stuff to test for such a CPP.  ./configure
    should fail if one is not available.

prototypes for most png_get_*() functions.