#94 pngtcl.h misinterprets missing CONST84

[Poor Yorick]

pngtcl.h states, " TIP 27 update. If CONST84 is not defined we are compiling
against a core before 8.4 and have to disable some CONST'ness." However newer
versions of tcl.h only define CONST86. Therefore, the conclusion pngtcl.h
draws is false. But the breakage actually comes because pngtcl.h itself
defines CONST84, causing tk.h not to define CONST84_RETURN, which then causes a
compilation error.

[Jan Nijtmans]

Schould be fixed now, in commit [r346]

[Jan Nijtmans]

Schould be fixed now, in commit [r436]