This reverts commit 2438825d.

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

"PNG_" to begin any of their own symbols.

argument names file_gamma, int_file_gamma, and srgb_intent consistently.

"png_ptr ptr" should be "png_structp png_ptr"

 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.

    to the manual. Removed the synopses from libpngpf.3 because they
    were out of date and no longer useful.  Better information can be
    obtained by reading the prototypes and comments in pngpriv.h

prototypes for most png_get_*() functions.

or an over-large compressed zTXt chunk with the progressive reader.

char_index, divisor, exp_b10, and gamma_val, respectively, and
changed exp() back to png_exp().

to avoid "shadow" warnings.  Revised png_fixed() in png.c to avoid compiler
warning about reaching the end without returning anything.