check for available space

[jlaffaye]

check if the required disk space is available before downloading and warn if it is not the case.

[bapt]

this is now done before fetch files, still needs to be done before installing things.

[emaste]

I am investigating pkg for use in upgrade / downgrade of $WORK's FreeBSD-based appliance and this is a key feature for us

[andrejzverev]

I'm sure if is done for 1.3 and later, can you confirm?

[bapt]

It is not done for installation