Should error out immediately if a perl version does not (yet) exist

[xtaran]

Trying to specify 5.24 currently results in the following error:

5.24 is not installed; attempting download
bzip2: (stdin) is not a bzip2 file.
tar: Child returned status 2
tar: Error is not recoverable: exiting now

But the build continues:

$ perlbrew use 5.24
ERROR: The installation "5.24" is unknown.
$ perl --version
This is perl 5, version 14, subversion 2 (v5.14.2) built for x86_64-linux-gnu-thread-multi

IMHO the whole build should stop if an error like tar: Error is not recoverable is encountered.

Example log: https://travis-ci.org/xtaran/unburden-home-dir/jobs/127297497
Example .travis.yml: https://github.com/xtaran/unburden-home-dir/blob/travis-tests/.travis.yml

[xtaran]

This actually also happens with dev instead of a explicit version number, see https://travis-ci.org/xtaran/unburden-home-dir/jobs/128909030#L108

Then again, it works fine if I use 5.24.0 instead of just 5.24.