Avoid sourcing .bashrc multiple times

This is achieved by setting and checking the variable _BASHRC_LOADED
when .bashrc is loaded.  To reload .bashrc, you can unset BASHRC_LOADED
first.
Don't set $TERM_PROGRAM in .bashrc
Change cursor in insert mode if using iTerm2
Add a bash function 'calc' for quick math

The function is just a wrapper around GNU bc.