error handling in linux is now unsuppressed.

However, so many err check is introduced. Some refactoring is needed.
remove mustParse on frebsd.
refactoring.
fix darwin mem_swap parse error.
fix getPagesize parse error.
fix darwin netstat format parsing error.
remove "mustParse" function on darwin.
fix error handling.
Merge pull request #16 from shirou/errorhandling

Errorhandling