py/formatfloat: Format all whole-number floats exactly.

Formerly, py/formatfloat would print whole numbers inaccurately with
nonzero digits beyond the decimal place.  This resulted from its strategy
of successive scaling of the argument by 0.1 which cannot be exactly
represented in floating point.  The change in this commit avoids scaling
until the value is smaller than 1, so all whole numbers print with zero
fractional part.

Fixes issue #4212.

Signed-off-by: Dan Ellis dan.ellis@gmail.com

tools/tinytest-codegen.py

@@ -79,6 +79,7 @@ exclude_tests = (
     "float/float_divmod.py",
     # requires double precision floating point to work
     "float/float2int_doubleprec_intbig.py",
+    "float/float_format_ints_doubleprec.py",
     "float/float_parse_doubleprec.py",
     # inline asm FP tests (require Cortex-M4)
     "inlineasm/asmfpaddsub.py",