Make the Python implementation of warnings compatible with the C implementation regarding non-callable showwarning

Use float constructors instead of magic code for float constants

the stack was being unwound by two levels instead of one each time.

An assertion in readline() would fail as data was already in the
internal buffer even though the socket was in unbuffered read mode.
That case is now handled.  More importantly, read() has been fixed to
not over-recv() and leave newly recv()d data in the _fileobject buffer.

The max() vs min() issue in read() is now gone.  Neither was correct.
On bounded reads, always ask recv() for the exact amount of data we
still need.

Candidate for backporting to release25-maint along with r62627.

Ippolito.

Closes issue #2750.

showwarning API. Turns out 'inspect' uses 'operator' which is an extension
module. That's a problem when it has not been built yet by setup.py.

that lacks support for the new 'line' argument.

characters. This avoids the common case of something like 'NUMBER(10)' not
being parsed as 'NUMBER', like expected. Also corrected the docs about
converter names being case-sensitive. They aren't any longer.

sqlite3.Row type is now correctly hashable.

#ifdefing was useless.

(as documented) rather than True and False.

at reducing the size of the diff between the 2.x decimal.py
and 3.x decimal.py and thereby making future merges easier:

- replace one instnace of an old-style raise statement
- define __div__ in terms of __truediv__ instead of the
  other way around
- make wording match on an exception message

'Context flags get set, not incremented'