[yafuse]: parse Ext4 extent tree and directory entry;
          show stat of Ext4 extent tree and directory entry;
[yafuse]: fix compiling warnings after '--enable-warnings' is set.
[yafuse]: fix compiling warnings after '--enable-warnings' is set.
[yafuse]: fix compiling warnings after '--enable-warnings' is set.
[yafuse]: set '--enable-warnings' as default;
          '-Wredundant-decls' and '-Wstrict-prototypes' are disused as compiling warnings.