NumberParser: try en-US too if parsing fails

If the parsing fails with the default locale, let's
arrogantly and ethnocentrically try again with en-US.
Test NumberParser more

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
NumberParserTest: added (failing) tests for faulty use-cases.

Signed-off-by: Jean-Yves Tinevez <jean-yves.tinevez@pasteur.fr>
NumberParser: for standard number format, try US locale first

For integers and fractional numbers using a decimal point, optionally
signed, we really want the result to be locale-independent.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Refactor the NumberFormatTest a bit

This should help point out the differences between the locales.

While at it, implement parsing of Infinity and NaN (fixing J-Y's tests).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>