Merge branch '1.2.x' into 1.3.x

* 1.2.x: (89 commits)
  t/: Add a test suite.
  ec.c: Don't lose error status when constructing points from a sequence.
  ec.c: Free partially constructed points coordinatewise.
  *.c: Be more careful about `PySequence_Size'.
  key.c: Reformat the rest of the `KeyError' constructor.
  key.c: Parse `KeyError' constructor arguments by hand.
  catacomb-python.h: Add a macro for raising `OverflowError'.
  key.c: Collect `KeyError' argument count as a separate step.
  key.c: Use tuple functions on `KeyError' argument tuple.
  key.c: Rename sad-path label to `end'.
  key.c: Delete duplicate setting of `errstring'.
  util.c (mkexc): Populate dictionary before constructing exception class.
  key.c: Only set the error code.
  catacomb.c, util.c: Publish negative constants correctly.
  field.c: Delete the completely unused `getfe' function.
  key.c (convfilter): Fix sense of error tests.
  buffer.c, ec.c: Fix required size for EC `buffer' encoding.
  algorithms.c: Fix `max' property name in docstrings.
  catacomb/__init__.py (_HashBase): Check that integers are within bounds.
  debian/rules: Build using the provided Makefile.
  ...