added skelton mode.
fixed a bug that the script tries to close unopened database.
make access to the database more efficient.
disabled -s option.
Preparation for implementation of levelDb backend.
switched database backend from sqlite3 to levelDb.
updated cxxtags for new db backend.
implement basic functions.
update a test.
implement "def" query.
implement basic functions.
update a test.
refactored.
change the database structure.
modify makefile
quit using comon database.
quit associative search when retrieve references.
renamed database which commonly used by all the compile units.
support parallel execution.
reduce sleep time to wait unlock of a database.