Log message:
Fix MASTER_SITES.

Log message:
Import py-construct-2.5.2 as devel/py-construct.
Originally packaged in pkgsrc-wip by Eric Schnoebelen and updated to the
latest stable version and minor (more or less) cosmetic fixes by myself.

Construct is a powerful declarative parser for binary data.

It is based on the concept of defining data structures in a declarative
manner, rather than procedural code: Simple constructs can be combined
hierarchically to form increasingly complex data structures. It's the
first library that makes parsing fun, instead of the usual headache it
is today.

Construct features bit and byte granularity, symmetrical operation
(parsing and building), component-oriented declarative design, easy
debugging and testing, an easy-to-extend subclass system, and lots of
primitive constructs to make your work easier.

        * Fields
        * Structs
        * Unions
        * Repeaters
        * Meta constructs
        * Switches
        * On-demand parsing
        * Pointers
        * And more!