support db config file for development environment.

when using uninstall and install scripts, you could specify a database config file as a command line argument. Or it will look for ${SITE_DIR}/dev_config/database.cfg file if no argument. The database.cfg file should like this:
defaultHost="localhost"
defaultPort="8889"
defaultUsername="root"
defaultMysqlPath="/Applications/MAMP/Library/bin/"

Add a line in .git/info/exclude file to let git ignore the config dir:
# git ls-files --others --exclude-from=.git/info/exclude
# Lines that start with '#' are comments.
# For a project mostly in C, the following would be a good set of
# exclude patterns (uncomment them if you want to use them):
# *.[oa]
# *~
.DS_Store
dev_config/