PNG_IO SvnCode

Version string changed to 4.5.1.

Minor formatting change in output, plus change to version number.

Added initialisation of IDAT_1 at line 250. This is to avoid an unitialized variable warning - the initial value is never used.

Removed redundant with/use, comment changes, pragma Assert to check chunk codes, instead of if then, plus changes to strings to describe colour type codes.

Removal of redundant with/use and many comment changes plus one or two minor changes.

Removed two redundant lower bound checks and one redundant type conversion.

Added representation clause for Rendering_Intent.

Removed redundant with and use clauses.

Removed redundant exception Give_Up.

Added colour type string function from png_dump.adb.