Program options default has unreasonable precision

Source code:
``` int i,e,t,d;
time_t now,then;
double tolerance,stageTolerance,areadone,rmsadj;
bool done=false;
string inputFile,outputFile;
bool validArgs,validCmd=true;
po::options_description generic("Options");
po::options_description hidden("Hidden options");
po::options_description cmdline_options;
po::positional_options_description p;
po::variables_map vm;
generic.add_options()
("tolerance,t",po::value(&tolerance)->default_value(0.1),"Vertical tolerance")
("output,o",po::value(&outputFile),"Output file");
hidden.add_options()
("input",po::value(&inputFile),"Input file");
p.add("input",1);
cmdline_options.add(generic).add(hidden);
//...
cout<

Start by reproducing the formatting with the shown Boost.Program_options configuration and inspect how default_value formats a double for the displayed option description. Compare the behavior with ldecimal.cpp in the linked bezitopo project, while preserving the requested 0.1 form rather than .1. Done means the default is displayed as (=0.1) without breaking other option output.

Scritto dal modello di indicizzazione a partire dal testo della issue.