Changeset 12f253c in rtems-source-builder

Download source from RTEMS if a release.

Download source from ftp.rtems.org before the package's URL if
a release.

If a user adds a URL via the command line that is used then the
RTEMS release path then the package's URL.

A user can add --url=​file://path/../morepath to have the RSB use
a local cache of source on their hard disk. This is useful if you
need to wipe the RSB and start again. Save away the 'sources' and
'patches' directories to a common directory and provide it with via
the --url option using the '​file://' prefix.

Closes #2482.