New ini-file feature: += appends RHS to LHS.

New ini-file feature: += appends RHS to LHS.
Added doxygen comments to inifile.hh.
Updated initest.  Some other minor cleanup.

base/inifile.cc:
    Add support for '+=' append operation.
    Factor common code from IniFile::load() and IniFile::add() into new Section::add().
    Rename ConfigTable to SectionTable (more descriptive).
    Fix bug in Section::dump().
base/inifile.hh:
    Add doxygen comments.
    Add support for '+=' append operation.
    Factor common code from IniFile::load() and IniFile::add() into new Section::add().
    Rename ConfigTable to SectionTable (more descriptive).
test/Makefile:
    initest needs cprintf.o now.
test/foo.ini:
    Add test of '+=' operator.
test/initest.cc:
    Bring this up-to-date.  Steal main loop from main.cc so we can test
    multiple .ini files and command-line assignments too.

--HG--
extra : convert_revision : 982521677fbf464e93aa93798ff7d9611826f17c