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When converting a number object to a string, luaO_tostring gets called,
which adds a "float mark" to floating point numbers that come out of
sprint looking like an int, to the effect that "0" becomes "0.0".

This can be turned off by defining LUA_COMPAT_FLOATSTRING.
luaconf.h says: "This macro is not on by default even in compatibility
mode, because this is not really an incompatibility."

I slightly disagree, as it introduces an incompatibility when using
different locales for output.

This example (expecting decimal comma representation)

    print( os.setlocale 'german' )
    print( 0.0, 0.1 )


    0       0,1

using Lua 5.2.4 and

    0.0     0,1

with Lua 5.3.0.

I had to learn that the hard way yesterday when my output containing
(floating point) zeros got severely borked. I *know* that using
unformatted output after switching to 5.3 means asking for some trouble,
but adding hard-coded '.0' to the number does not look like a sensible
default to me.