program_options should understand "inf" and "nan"

[Rhys Ulerich <rhys.ulerich@…>]

program_options does not accept NaN or Inf as valid double input. This problem seems like it will be fixed automatically when #5689 arrives in 1.48. I am setting the milestone accordingly.

Recreate: the following sequence modifies the "Getting Started" first.cpp to accept double input:

   cp $BOOST_SOURCE/libs/program_options/example/first.cpp .
   perl -pi -e 's/<int>/<double>/;' first.cpp
   LDFLAGS="-lboost_program_options" make first # ...or whatever

The modified example indeed barfs on NaN or Inf input:

   $ ./first --compression=5.5
   Compression level was set to 5.5.

   $ ./first --compression=Inf
   error: in option 'compression': invalid option value 'Inf'

   $ ./first --compression=NaN
   error: in option 'compression': invalid option value 'NaN'

[Vladimir Prus]

This indeed appears to be fixed automatically due to lexical_cast fixes. The example in the issue works for me on SVN HEAD.