Store the status exactly once on the HTTPRedirect

[jaraco]

While reviewing #1611, I noticed that the 'status' of an HTTPRedirect is stored in two places on the class, once in the Exception.args and again in the HTTPRedirect.status. This approach is sloppy, and could lead to situations where the two values don't match. Better would be to either store the value in the args and refer to it when referencing the status (as proposed here) or to only store it in the status property. I feel like this proposed change is less invasive than removing the status from the args.

One backward-incompatible effect this proposal introduces is that the status can no longer be set after the redirect is constructed:

r = HTTPRedirect('/go-here')
r.status = 302

Previously, that would have worked but no longer will. I suggest this usage was never supported (not captured in tests) and so may be changed without formally introducing a backward-incompatibility.

I don't feel strongly about one approach or another, but I do feel strongly that this status should be stored exactly once.

[codecov]

Codecov Report

Merging #1615 into master will increase coverage by 0.24%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1615      +/-   ##
==========================================
+ Coverage    76.7%   76.94%   +0.24%     
==========================================
  Files         106      106              
  Lines       14280    14374      +94     
==========================================
+ Hits        10953    11060     +107     
+ Misses       3327     3314      -13

Impacted Files	Coverage Δ
cherrypy/_cperror.py	94.41% <100%> (-0.17%)	⬇️
cherrypy/lib/gctools.py	35.03% <0%> (-48.91%)	⬇️
cherrypy/lib/jsontools.py	80.55% <0%> (-2.78%)	⬇️
cherrypy/test/test_refleaks.py	95% <0%> (-2.5%)	⬇️
cherrypy/test/webtest.py	56.84% <0%> (-1.47%)	⬇️
cherrypy/lib/reprconf.py	86.43% <0%> (-0.64%)	⬇️
cherrypy/test/test_conn.py	90.36% <0%> (-0.37%)	⬇️
cherrypy/lib/httpauth.py	78.81% <0%> (-0.32%)	⬇️
cherrypy/_cpconfig.py	77.1% <0%> (-0.28%)	⬇️
cherrypy/_cpdispatch.py	92.46% <0%> (-0.27%)	⬇️
... and 53 more

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