This makes the beginning of all files the same and a little simpler.
`${0%/*}` turns "/home/user/repository/bin/blackbox_edit" into
"/home/user/repository/bin", exactly like basename but without eating a
process.
Because other scripts needed `$blackbox_home` I made this into a
standardard variable that's always available.
This also loads _stack_lib.sh always because _blackbox_common.sh
requires it.
* Using $BASEDIR to pass the location of the repo hasn't worked for a
while. It has been removed. Simply cd into the vcs repo before
running a command.
BUG FIXES:
* .gitignore was being created in subdirectories instead of VCS root.
MINOR CHANGES
* _blackbox_common.sh: Replace change_to_root with change_to_vcs_root
* confidence_test.sh: Added more assertions and tests.
