updateBoost.sh doesn't work on macOS because 'dirname' doesn't have '--version' option

[seanm]

@thewtex KWSys's updateBoost.sh script doesn't work on macOS because the macOS 'dirname' doesn't have a '--version' option.

Perhaps there is a different way to check that dirname exists?

If I remove that 'validate' section of code, the script then works.

[thewtex]

@seanm A better option may be the type built-in from bash:

https://stackoverflow.com/questions/592620/check-if-a-program-exists-from-a-bash-script

[seanm]

On my Mac:

leprechaun:Desktop sean$ type dirname
dirname is /usr/bin/dirname